Serum VEGF increases in diabetic polyneuropathy, particularly in the neurologically active symptomatic stage

AIM

To identify the relationship between vascular endothelial growth factor (VEGF) and diabetic polyneuropathy (DPN).

METHODS

Two hundred and twenty diabetic patients participated, 113 with DPN and 107 without DPN. All patients were also classified according to the four stages of DPN (no neuropathy: stage 0; asymptomatic neuropathy: stage 1; symptomatic neuropathy: stage 2; disabling neuropathy: stage 3). Serum VEGF concentration was measured using an enzyme-linked immunosorbent assay (ELISA) and levels between the patients with and without DPN and also between the different stages of DPN, were compared.

RESULTS

The mean serum VEGF level in all patients was 264.6 +/- 218.8 pg/ml. The mean serum VEGF level was higher in patients with DPN (310.1 +/- 224.3 pg/ml) than in the patients without DPN (216.5 +/- 204.0 pg/ml, P = 0.0014). Serum VEGF was higher in the 'symptomatic' stage (stage 2, 364.8 +/- 225.9 pg/ml) in comparison with the 'asymptomatic' (stage 1, 256.7 +/- 224.4 pg/ml, P = 0.015) and 'disabling' (stage 3, 180.3 +/- 109.4 pg/ml, P = 0.042) stages. The mean serum VEGF level in patients with diabetic retinopathy (261.1 +/- 210.6 pg/ml) and in patients with diabetic nephropathy (241.5 +/- 185.7 pg/ml) was not increased.

CONCLUSIONS

The serum VEGF level is increased in patients with DPN, particularly in patients in the neurologically active 'symptomatic' stage.

A leptomycin B resistance gene ofSchizosaccharomyces pombeencodes a protein similar to the mammalian P-glycoproteins

Screening for leptomycin B (LMB)-resistant transformants in a gene library constructed in Schizosaccharomyces pombe with the chromosomal DNA of an LMB-resistant mutant of S. pombe and with multicopy plasmid pDB248' as the vector led to the isolation of a gene, named pmd1+, encoding a 1362-amino-acid protein. This protein showed great similarity in amino acid sequence to the mammalian P-glycoprotein encoded by the multidrug resistance gene, mdr, and the Saccharomyces cerevisiae a-factor transporter encoded by STE6. In addition, computer analyses predicted that the protein encoded by pmd1+ formed an intramolecular duplicated structure and each of the halves contained six transmembrane regions as well as two ATP-binding domains, as observed with the P-glycoproteins and the STE6 product. Consistent with this was that S. pombe cells containing the pmd1+ gene on a multicopy plasmid showed resistance not only to LMB but also to several cytotoxic agents. The pmd1 null mutants derived by gene disruption were viable and hypersensitive to these agents. All these data suggest that the pmd1+ gene encodes a protein that is a structural and functional counterpart of mammalian mdr proteins.

Regulation of SV40 large T-antigen stability by reversible acetylation

Reversible acetylation on protein lysine residues has been shown to regulate the function of both nuclear proteins such as histones and p53 and cytoplasmic proteins such as alpha-tubulin. To identify novel acetylated proteins, we purified several proteins by the affinity to an anti-acetylated-lysine antibody from cells treated with trichostatin A (TSA). Among the proteins identified, here we report acetylation of the SV40 large T antigen (T-Ag). The acetylation site was determined to be lysine-697, which is located adjacent to the C-terminal Cdc4 phospho-degron (CPD). Overexpression of the CBP acetyltransferase acetylated T-Ag, whereas HDAC1, HDAC3 and SIRT1 bound and deacetylated T-Ag. The acetylation and deacetylation occurred independently of p53, a binding partner of T-Ag, but the acetylation was enhanced in the presence of p53. T-Ag in the cells treated with TSA and NA or the acetylation mimic mutant (K697Q) became unstable in COS-7 cells, suggesting that acetylation regulates stability of T-Ag. Indeed, NIH3T3 cells stably expressing K697Q showed decreased anchorage-independent growth compared with those expressing wild type or the K697R mutant. These results demonstrate that acetylation destabilizes T-Ag and regulates the transforming activity of T-Ag in NIH3T3 cells.

Gene expression of Corynebacterium glutamicum in response to the conditions inducing glutamate overproduction

AIM

The ultimate aim is to elucidate the molecular mechanisms for glutamate overproduction by Corynebacterium glutamicum.

METHODS AND RESULTS

Gene expression in response to the conditions inducing glutamate overproduction was investigated by using a DNA microarray technique. Most genes involved in the EMP pathway, the PPP, and the TCA cycle were downregulated, while five genes that were highly upregulated (NCgl0917, NCgl2944, NCgl2945, NCgl2946, and NCgl2975) were identified under all the three conditions for overproduction that are studied here. Gene products of NCgl2944, NCgl2945, and NCgl2946 were highly homologous to each other, did not resemble any other protein, and have remained uncharacterized thus far. The product of NCgl0917 showed a similarity to a few hypothetical and uncharacterized proteins. NCgl2975 was homologous to metal-binding proteins.

CONCLUSIONS

The decrease in the activity of 2-oxoglutarate dehydrogenase complex, a key enzyme that is downregulated during glutamate overproduction, can be mainly attributed to the downregulation of odhA and sucB. Five highly upregulated genes were also identified.

SIGNIFICANCE AND IMPACT OF THE STUDY

Although fermentative production of glutamate has been carried out for more than 45 years, information on the molecular mechanisms of glutamate overproduction is still limited. This study further elucidates these mechanisms.

Protein serine/threonine kinases in signal transduction for secondary metabolism and morphogenesis in Streptomyces

A number of proteins in the Gram-positive bacterial genus Streptomyces are phosphorylated on their serine/threonine and tyrosine residues in response to developmental phases. AfsR is one of these proteins and acts as a transcriptional factor in both the regulation of secondary metabolism in Streptomyces coelicolor A3(2) and morphological differentiation in Streptomyces griseus. In S. coelicolor A3(2), AfsR is phosphorylated on its serine and threonine residues by more than three protein kinases whose kinase activity is enhanced by means of autophosphorylation on their serine and threonine residues. The degree of autophosphorylation of AfsK is regulated by KbpA which, by binding directly to the kinase domain of AfsK, inhibits its autophosphorylation. Phosphorylation of AfsR enhances its DNA-binding activity and causes it to bind the promoter elements, including -35, of afsS, thus resulting in activation of afsS transcription. ATPase activity of AfsR is essential for this transcriptional activation, probably because the energy available from ATP hydrolysis is required for the isomerization of the closed complex between AfsR and RNA polymerase to a transcriptionally competent open complex. afsS, encoding a 63-amino-acid protein, then activates transcription of actII-ORF4, a pathway-specific transcriptional activator in the actinorhodin biosynthetic gene cluster, in an as yet unknown way. Distribution of the afsK- afsR systems in a wide variety of Streptomyces species and the presence of many phosphorylated proteins in a given Streptomyces strain suggest that the signal transduction via not only two-component regulatory systems but also serine/threonine kinases generally regulates secondary metabolism and morphogenesis in this genus.

Radicicol binding to Swo1/Hsp90 and inhibition of growth of specific temperature-sensitive cell cycle mutants of fission yeast

A panel screening using cdc mutants of Schizosaccharomyces pombe identified radicicol as a potent growth inhibitor of certain mutants at the permissive temperature. The strains sensitive to radicicol were cdc7, cdc11, and cdc14, all of which are defective in early septum formation. Cytokinesis but not nuclear division of these mutants was inhibited by radicicol, but that of cells with the wild-type background was not. A biologically active derivative of radicicol with a biotin moiety at the C-11 position bound Swo1, an Hsp90 homologue in S. pombe. Increased Swo1 expression partially suppressed radicicol sensitivity of cdc14 and almost completely rescued morphological abnormalities in cdc14 and cdc7 cells induced by radicicol at the permissive temperature. On the other hand, the increased Swo1 expression did not restore septum formation at the nonpermissive temperature. These results suggest that Swo1, as a molecular chaperone, plays a role in stabilizing these temperature-sensitive proteins at the permissive temperature or in activating the cytokinesis signaling cascade.

Oxygenation reactions of various tricyclic fused aromatic compounds using Escherichia coli and Streptomyces lividans transformants carrying several arene dioxygenase genes

Bioconversion (biotransformation) experiments on arenes (aromatic compounds), including various tricyclic fused aromatic compounds such as fluorene, dibenzofuran, dibenzothiophene, carbazole, acridene, and phenanthridine, were done using the cells of Escherichia coli transformants expressing several arene dioxygenase genes. E. coli carrying the phenanthrene dioxygenase (phdABCD) genes derived from the marine bacterium Nocardioides sp. strain KP7 converted all of these tricyclic aromatic compounds, while E. coli carrying the Pseudomonas putida F1 toluene dioxygenase (todC1C2BA) genes or the P. pseudoalcaligenes KF707 biphenyl dioxygenase (bphA1A2A3A4) genes was not able to convert these substrates. Surprisingly, E. coli carrying hybrid dioxygenase (todC1::bphA2A3A4) genes with a subunit substitution between the toluene and biphenyl dioxygenases was able to convert fluorene, dibenzofuran, and dibenzothiophene. The cells of a Streptomyces lividans transformant carrying the phenanthrene dioxygenase genes were also evaluated for bioconversion of various tricyclic fused aromatic compounds. The ability of this actinomycete in their conversion was similar to that of E. coli carrying the corresponding genes. Products converted from the aromatic compounds with these recombinant bacterial cells were purified by column chromatography on silica gel, and identified by their MS and 1H and 13C NMR analyses. Several products, e.g., 4-hydroxyfluorene converted from fluorene, and cis-1,2-dihydroxy-1,2-dihydrophenanthridine, cis-9,10-dihydroxy-9,10-dihydrophenanthridine, and 10-hydroxyphenanthridine, which were converted from phenanthridine, were novel compounds.

Autophosphorylation of a bacterial serine/threonine kinase, AfsK, is inhibited by KbpA, an AfsK-binding protein

A protein serine/threonine kinase, AfsK, and its target protein AfsR globally control physiological and morphological differentiation in the bacterial genus Streptomyces. A protein (KbpA) of 252 amino acids encoded by an open reading frame in a region upstream of afsK in Streptomyces coelicolor A3(2) was identified as an AfsK-interacting protein. The interaction site of AfsK was in the N-terminal portion containing the kinase catalytic domain. KbpA bound a nonphosphorylated form of AfsK and inhibited its autophosphorylation at serine and threonine residues. KbpA in the reaction mixture containing AfsK and AfsR also inhibited the phosphorylation of AfsR by AfsK, presumably because KbpA inhibited the conversion from the inactive, nonphosphorylated form of AfsK to the active, phosphorylated form. kbpA was transcribed throughout growth, and the transcription was enhanced when production of actinorhodin had already started. KbpA thus appeared to play an inhibitory role in a negative feedback system in the AfsK-AfsR regulatory pathway. Consistent with these in vitro observations, kbpA served as a repressor for actinorhodin production in S. coelicolor A3(2); disruption of kbpA greatly enhanced actinorhodin production, and overexpression of kbpA reduced the production.

The A-factor regulatory cascade and cAMP in the regulation of physiological and morphological development in Streptomyces griseus

In the A-factor regulatory cascade leading to the onset of streptomycin biosynthesis and aerial mycelium formation in Streptomyces griseus, the A-factor receptor protein (ArpA) serves as a DNA-binding repressor and A-factor releases the repression by binding to ArpA and dissociating it from the DNA. Mutants defective in arpA therefore produce streptomycin and aerial hyphae in the absence of A-factor. A gene that inhibits streptomycin production and aerial hyphae formation in an arpA mutant was cloned on a high-copy-number plasmid and found to encode a eukaryotic-type adenylate cyclase (CyaA). Consistent with this, an exogenous supply of cAMP at high concentration almost abolished streptomycin production and aerial hyphae formation. On the other hand, cAMP at lower concentrations stimulated or accelerated these developmental processes. The effects of cAMP were detectable only in arpA mutants, and not in the wild -type strain; an exogenous supply of cAMP or cyaA disruption in the wild-type strain caused almost no effect on these phenotypes. Thus the effects of cAMP became apparent only in the arpA-defective background. cAMP at high concentrations inhibited stringent response factor ppGpp production, which is important for the onset of antibiotic biosynthesis. cAMP also influenced the timing of tyrosine phosphorylation of more than nine proteins. These findings show that a cAMP regulatory relay for physiological and morphological development functions in a concerted and interdependent way with other signal transduction pathways.

Biotransformation of phenanthrene and 1-methoxynaphthalene with Streptomyces lividans cells expressing a marine bacterial phenanthrene dioxygenase gene cluster

The phdABCD gene cluster in a marine bacterium Nocardioides sp. strain KP7 codes for the multicomponent enzyme phenanthrene dioxygenase. phdA encoding an iron-sulfur protein large subunit alpha, phdB encoding its small subunit beta, phdC encoding ferredoxin, and phdD encoding ferredoxin reductase, were replaced in such a way that the termination codons of the preceding open reading frames were overlapped with the initiation codons of the following genes. This manipulated phdABCD gene cluster was positioned downstream of the thiostrepton-inducible promoter PtipA in a high-copy-number vector pIJ6021, and introduced into the gram-positive, soil-inhabiting, filamentous bacterium Streptomyces lividans. The recombinant S. lividans cells converted phenanthrene into a cis-diol form, which was determined to be cis-3,4-dihydroxy-3,4-dihydrophenanthrene by its UV spectral data as well as HPLC property, using the authentic sample for comparison. This biotransformation proceeded very efficiently; 200 microM and 2 mm of phenanthrene were almost completely converted to its cis-diol form in 6 h and 32 h, respectively. In addition, the S. lividans cells carrying the phdABCD gene cluster were found to transform 1-methoxynaphthalene to two products, which were identified to be 8-methoxy-2-naphthol in addition to 8-methoxy-1,2-dihydro-1,2-naphthalenediol by their EI-MS, 1H- and 13C-NMR spectral data.

Histone deacetylase as a new target for cancer chemotherapy

Trichostatin A (TSA) and trapoxin (TPX), inhibitors of the eukaryotic cell cycle and inducers of morphological reversion of transformed cells, inhibit histone deacetylase (HDAC) at nanomolar concentrations. Recently, FK228 (also known as FR901228 and depsipeptide) and MS-275. antitumor agents structurally unrelated to TSA, have been shown to be potent HDAC inhibitors. These inhibitors activate the expression of p21Waf1 in a p53-independent manner. Changes in the expression of regulators of the cell cycle, differentiation, and apoptosis with increased histone acetylation may be responsible for the cell cycle arrest and antitumor activity of HDAC inhibitors. TSA has been suggested to block the catalytic reaction by chelating a zinc ion in the active site pocket through its hydroxamic acid group. On the other hand, an epoxyketone has been suggested to be the functional group of TPX capable of alkylating the enzyme. We synthesized a novel TPX analogue containing a hydroxamic acid instead of the epoxyketone. The hybrid compound, called cyclic hydroxamic-acid-containing peptide 1 (CHAP1) inhibited HDAC at low nanomolar concentrations. The HDAC1 inhibition by CHAPI was reversible, as is that by TSA, in contrast to irreversible inhibition by TPX. Interestingly, HDAC6, but not HDAC1 or HDAC4, was resistant to TPX and CHAP1, while TSA inhibited these HDACs to a similar degree. CHAP31, the strongest HDAC inhibitor obtained from a variety of CHAP derivatives, exhibited antitumor activity in BDF1 mice bearing B16/BL6 tumor cells. These results suggest that CHAP31 is promising as a novel therapeutic agent for cancer treatment, and that CHAP may serve as a basis for new HDAC inhibitors and be useful for combinatorial synthesis and high-throughput screening.

Cyclic hydroxamic-acid-containing peptide 31, a potent synthetic histone deacetylase inhibitor with antitumor activity

Cyclic hydroxamic-acid-containing peptide 1 (CHAP1), designed as a hybrid of trichostatin A and trapoxin, is a lead compound for the development of potent inhibitors of histone deacetylase (HDAC). In this study, we synthesized a series of CHAP derivatives and evaluated their biological activities by monitoring the potency of their inhibition of HDAC activity, their ability to augment the expression of MHC class-I molecules in B16/BL6 cells, and their effect on cell proliferation. A structure-activity relationship study using these three assay systems revealed several requirements of their structure for the strong inhibition of HDAC not only in the cell-free situation, but also in cells. When the structures of CHAP derivatives are represented as cyclo(-Asu(NHOH)-AA(2)-AA(3)-Pro or Pip-)(n), where Asu(NHOH) and Pip are zeta-hydroxamide-alpha-aminosuberic acid and pipecolic acid, respectively, (a) the tetrapeptide structure (n = 1) was better than the octapeptide one (n = 2); (b) AA(2) and AA(3) should be hydrophobic; and (c) the combination of amino acid chirality should be LDLD for the strongest inhibition of HDAC in cells (LDLD > LLLD, LDLL > LLDL). cyclo(-L-Asu(NHOH)-D-Tyr(Me)-L-Ile-D-Pro-) or CHAP31 was selected as one of the strongest CHAPs, and its biological activity was characterized further. CHAP31 was much more stable in the presence of cultured cells (t(1/2) > 3000 h) than trichostatin A (t(1/2) = 14.7 h) or trapoxin A (t(1/2) = 2.10 h). CHAP31 exhibited antitumor activity in C57BL x DBA/2 F(1) (BD2F(1)) mice bearing B16/BL6 tumor cells. Furthermore, CHAP31 inhibited the growth in four of five human tumor lines implanted into nude mice. These results suggest CHAP31 to be promising as a novel therapeutic agent for cancer treatment.

A role for Hsc70 in regulating nucleocytoplasmic transport of a temperature-sensitive p53 (p53Val-135)

Mouse temperature-sensitive p53(Val-135) accumulates in the nucleus and acts as a "wild-type" at 32 degrees C while it is sequestered in the cytoplasm at 37 degrees C. The cytoplasmic p53(Val-135) relocalized into the nucleus upon inhibition of the nuclear export at 37 degrees C, whereas a mutation in a major bipartite nuclear localization signal (NLS) caused constitutive cytoplasmic localization, indicating that it shuttled between the cytoplasm and the nucleus by its own nuclear export signal and NLS rather than tethered to cytoplasmic structures. Although the full-length p53(Val-135) did not bind the import receptor at 37 degrees C, a C-terminally truncated p53(Val-135) lacking residues 326-390 did bind it. Molecular chaperones such as Hsc70 were associated with p53(Val-135) at 37 degrees C but not at 32 degrees C. When the nuclear export was blocked by leptomycin B, only a fraction lacking Hsc70 was specifically accumulated in the nucleus. Immunodepletion of Hsc70 from the reticulocyte lysate caused p53(Val-135) to bind the import receptor. This binding was blocked by supplying the cell extract containing Hsc70 but not by the addition of recombinant Hsc70 alone. We suggest that the association with the Hsc70-containing complex prevents the NLS from the access of the import receptor through the C-terminal region of p53(Val-135) at 37 degrees C, whereas its dissociation at 32 degrees C allows rapid nuclear import.

Replacements of amino acid residues at subsites and their effects on the catalytic properties of Rhizomucor pusillus pepsin, an aspartic proteinase from Rhizomucor pusillus

Site-directed mutagenesis was carried out to investigate the functional roles of amino acid residues of Rhizomucor pusillus pepsin (RMPP) in substrate-binding and catalysis. Mutations of two amino acid residues, E13 in the S3 subsite and N219 in the S3/S4 subsites, caused marked changes in kinetic parameters for two substrate peptides with different sequences. Further site-directed mutagenesis at E13 suggested that E13 plays a critical role in forming the correct hydrogen bond network around the active center. In the crystal structure of Rhizomucor miehei pepsin (RMMP), which is an aspartic proteinase produced by Rhizomucor miehei and shows 81% amino acid identity to RMPP, the Oepsilon atom of N219 forms a hydrogen bond with the N-H of isovaline in pepstatin A, a statine-type inhibitor, at the P3 position, suggesting that the loss of the hydrogen bond causes an unfavorable arrangement of the P3 residue. Among the mutants constructed, the E13A mutant showed a 5-fold increase in the ratio of clotting versus proteolytic activity without significant loss of clotting activity. This mutant may present a promising candidate for a useful milk coagulant.

Potent histone deacetylase inhibitors built from trichostatin A and cyclic tetrapeptide antibiotics including trapoxin

Trichostatin A (TSA) and trapoxin (TPX) are potent inhibitors of histone deacetylases (HDACs). TSA is proposed to block the catalytic reaction by chelating a zinc ion in the active-site pocket through its hydroxamic acid group. On the other hand, the epoxyketone is suggested to be the functional group of TPX capable of alkylating the enzyme. We synthesized a novel TPX analogue containing a hydroxamic acid instead of the epoxyketone. The hybrid compound cyclic hydroxamic acid-containing peptide (CHAP) 1 inhibited HDAC1 at low nanomolar concentrations. The HDAC1 inhibition by CHAP1 was reversible as it was by TSA, in contrast to the irreversible inhibition by TPX. CHAP with an aliphatic chain length of five, which corresponded to that of acetylated lysine, was stronger than those with other lengths. These results suggest that TPX is a substrate mimic and that the replacement of the epoxyketone with the hydroxamic acid converted TPX to an inhibitor chelating the zinc like TSA. Interestingly, HDAC6, but not HDAC1 or HDAC4, was resistant to TPX and CHAP1, whereas TSA inhibited these HDACs to a similar extent. HDAC6 inhibition by TPX at a high concentration was reversible, probably because HDAC6 is not alkylated by TPX. We further synthesized the counterparts of all known naturally occurring cyclic tetrapeptides containing the epoxyketone. HDAC1 was highly sensitive to all these CHAPs much more than HDAC6, indicating that the structure of the cyclic tetrapeptide framework affects the target enzyme specificity. These results suggest that CHAP is a unique lead to develop isoform-specific HDAC inhibitors.

A sigmaB-like factor responsible for carotenoid biosynthesis in Streptomyces griseus

Self-cloning experiments with a high-copy-number plasmid and Streptomyces griseus IFO13350 led to the cloning of a 11-kb DNA fragment that conferred yellow pigment production on the host. The cloned fragment contained a gene cluster for carotenoid biosynthesis, in which two polycistrons, crtE (encoding geranylgeranyl pyrophosphate synthase)-crtI (phytoene dehydrogenase)-crtB (phytoene synthase)-crtV (functionally unknown methyltransferase-like protein) and crtY (lycopene cyclase)-crtT (functionally unknown methyltransferase-like protein)-crtU (beta-carotene dehydrogenase), were present in a convergent way. Since strain IFO13350 produced no detectable amount of carotenoids, an increase in the copy number of the crt gene cluster led to production of carotenoids at a detectable level. Overexpression of the stress-responsive sigmaB-like protein CrtS from Streptomyces setonii also activated the cryptic crt genes in S. griseus and conferred pigmentation. A CrtS homologue (sigmaCrtS) in S. griseus, which was predicted by a computer-aided homology search, caused carotenogenesis to the same extent as CrtS of S. setonii, indicating that the two sigmaB-like proteins were functionally the same. Yellow pigment production by S. griseus containing crtS under the control of a strong promoter on a high-copy-number plasmid resulted from activation of transcription of the crt genes, because overexpression of sigmaCrtS in S. griseus led to transcriptional activation of the promoters in front of crtE and crtY. S1 nuclease mapping showed that crtS itself was transcribed at a low level under the laboratory conditions, which may account for undetectable production of carotenoids. The crt genes were suggested to locate very near one end of the linear chromosome, since they were completely deleted in mutant HH1 having large deletions at both ends. The gene organization of crt in S. griseus is similar to that in S. coelicolor A3(2) where the whole crt gene set is near one end of the chromosome.

A calcium-binding protein with four EF-hand motifs in Streptomyces ambofaciens

A gene (cabA) encoding a calcium-binding protein was cloned from Streptomyces ambofaciens. CabA was 180 amino acid residues long and contained four typical EF-hand motifs bearing high sequence similarity to the calcium-binding sites in calmodulin. Consistent with this, CabA showed distinct calcium-binding activity, comparable to bovine brain calmodulin. cabA was transcribed throughout growth, as found by S1 nuclease mapping. Southern hybridization experiments showed that a single copy of cabA was present in various Streptomyces species. A hypothetical relationship between CabA and aerial mycelium formation in this strain was examined, since S. ambofaciens showed calcium-dependent aerial mycelium formation. However, disruption of cabA or overexpression of cabA in S. ambofaciens caused no detectable phenotypic changes.

Radicicol binds and inhibits mammalian ATP citrate lyase

Six different biotinylated radicicol derivatives were synthesized as affinity probes for identification of cellular radicicol-binding proteins. Derivatives biotinylated at the C-17 (BR-1) and C-11 (BR-6) positions retained the activity of morphological reversion in v-src-transformed 3Y1 fibroblasts. Two radicicol-binding proteins, 120 and 90-kDa in size, were detected in HeLa cell extracts by employing BR-1 and BR-6, respectively. The 90-kDa protein bound to BR-6 was identified to be Hsp90 by immunoblotting. The 120-kDa protein bound to BR-1 was purified from rabbit reticulocyte lysate, and its internal amino acid sequence was identical to that of human and rat ATP citrate lyase. The identity of the 120-kDa protein as ATP citrate lyase was confirmed by immunoblotting. Interaction between BR-1 and ATP citrate lyase was blocked by radicicol but not by herbimycin A that interacts with Hsp90. These results suggest that radicicol binds the two proteins through different molecular portions of its structure. BR-1-bound ATP citrate lyase isolated from rabbit reticulocyte lysate showed no enzymatic activity. The activity of rat liver ATP citrate lyase was inhibited by radicicol and BR-1 but not by BR-6. Kinetic analysis demonstrated that radicicol was a non-competitive inhibitor of ATP citrate lyase with K(i) values for citrate and ATP of 13 and 7 microm, respectively.

Genetic and biochemical characterization of a protein phosphatase with dual substrate specificity in Streptomyces coelicolor A3(2)

A gene encoding a protein phosphatase (SppA) with a phosphoesterase motif, which was predicted by the genome project of the Gram-positive bacterium Streptomyces coelicolor A3(2), was cloned by PCR in pET32a(+) and expressed in Escherichia coli. SppA fused to thioredoxin (TRX-SppA) showed distinct heat-stable phosphatase activity toward p-nitrophenyl phosphate with optimal pH 8.0 and optimal temperature 55 degrees C. Mn2+ greatly enhanced enzyme activity, as is found with other protein Ser/Thr phosphatases. TRX-SppA was not inhibited by sodium orthovanadate or okadaic acid, both of which are known to be specific inhibitors of protein phosphatases. TRX-SppA showed phosphatase activity toward not only phosphoThr (pThr) and pTyr but also oligopeptides containing pSer, pThr, and pTyr, indicating that SppA is a protein phosphatase with dual substrate specificity. Disruption of the chromosomal sppA gene resulted in severe impairment of vegetative growth. All of these observations show that SppA, a protein phosphatase with dual specificity, plays an important, but not essential, role in vegetative growth of S. coelicolor A3(2). The presence of a single copy of sppA in all the 13 Streptomyces species examined, as determined by Southern hybridization, suggests a common role of SppA in general in Streptomyces species.

Mechanism of cell cycle arrest caused by histone deacetylase inhibitors in human carcinoma cells

Inhibitors of histone deacetylase (HDAC) block cell cycle progression at G1 in many cell types. We investigated the mechanism by which trichostatin A (TSA), a specific inhibitor of HDAC, induces G1 arrest in human cervix carcinoma HeLa cells. TSA treatment induced histone hyperacetylation followed by growth arrest in G as well as hypophosphorylation of pRb. The Cdk4 kinase activity was essentially unchanged during the TSA-induced G1 arrest. On the other hand, the arrest was accompanied by down-regulation of kinase activity of Cdk2, although the total protein levels of Cdk2 and its activator Cdc25A were unaffected. Upon TSA treatment, amounts of cyclin E and the CDK inhibitor p21WAF1/Cip1 were markedly increased, while that of cyclin A was reduced. The induction of p21 and down-regulation of cyclin A correlated well with the decreased Cdk2 activity and cell cycle arrest. Furthermore, gel filtration chromatography showed the association of p21 with the cyclin E-Cdk2 complex, suggesting that the activation of Cdk2 by the enhanced expression of cyclin E is blocked by the increased p21. The elevated expression of p2 is also observed in cells treated with trapoxin and FR901228, structurally unrelated histone deacetylase inhibitors. A human colorectal carcinoma cell line lacking both alleles of the p21 gene (p21-/-) was resistant to TSA several times more than the parental line (p21+/+). These results suggest that the suppression of Cdk2 kinase activity due to p21 overexpression play a critical role in HDAC inhibitor-induced growth inhibition.

Catalytic roles for two water bridged residues (Asp-98 and His-255) in the active site of copper-containing nitrite reductase

Two active site residues, Asp-98 and His-255, of copper-containing nitrite reductase (NIR) from Alcaligenes faecalis have been mutated to probe the catalytic mechanism. Three mutations at these two sites (D98N, H255D, and H255N) result in large reductions in activity relative to native NIR, suggesting that both residues are involved intimately in the reaction mechanism. Crystal structures of these mutants have been determined using data collected to better than 1. 9-A resolution. In the native structure, His-255 Nepsilon2 forms a hydrogen bond through a bridging water molecule to the side chain of Asp-98, which also forms a hydrogen bond to a water or nitrite oxygen ligated to the active site copper. In the D98N mutant, reorientation of the Asn-98 side chain results in the loss of the hydrogen bond to the copper ligand water, consistent with a negatively charged Asp-98 directing the binding and protonation of nitrite in the native enzyme. An additional solvent molecule is situated between residues 255 and the bridging water in the H255N and H255D mutants and likely inhibits nitrite binding. The interaction of His-255 with the bridging water appears to be necessary for catalysis and may donate a proton to reaction intermediates in addition to Asp-98.

An A-factor-dependent extracytoplasmic function sigma factor (sigma(AdsA)) that is essential for morphological development in Streptomyces griseus

A-factor (2-isocapryloyl-3R-hydroxymethyl-gamma-butyrolactone) at an extremely low concentration triggers streptomycin production and aerial mycelium formation in Streptomyces griseus. A-factor induces the expression of an A-factor-dependent transcriptional activator, AdpA, essential for both morphological and physiological differentiation by binding to the A-factor receptor protein ArpA, which has bound and repressed the adpA promoter, and dissociating it from the promoter. Nine DNA fragments that were specifically recognized and bound by histidine-tagged AdpA were isolated by cycles of a gel mobility shift-PCR method. One of them was located in front of a gene encoding an extracytoplasmic function sigma factor belonging to a subgroup of the primary sigma(70) family. The cloned gene was named AdpA-dependent sigma factor gene (adsA), and the gene product was named sigma(AdsA). Transcription of adsA depended on A-factor and AdpA, since adsA was transcribed at a very low and constant level in an A-factor-deficient mutant strain or in an adpA-disrupted strain. Consistent with this, transcription of adsA was greatly enhanced at or near the timing of aerial hyphae formation, as determined by low-resolution S1 nuclease mapping. High-resolution S1 mapping determined the transcriptional start point 82 nucleotides upstream of the translational start codon. DNase I footprinting showed that AdpA bound both strands symmetrically between the transcriptional start point and the translational start codon; AdpA protected the antisense strand from positions +7 to +41 with respect to the transcriptional start point and the sense strand from positions +12 to +46. A weak palindrome was found in the AdpA-binding site. The unusual position bound by AdpA as a transcriptional activator, in relation to the promoter, suggested the presence of a mechanism by which AdpA activates transcription of adsA in some unknown way. Disruption of the chromosomal adsA gene resulted in loss of aerial hyphae formation but not streptomycin or yellow pigment production, indicating that sigma(AdsA) is involved only in morphological development and not in secondary metabolic function. The presence of a single copy in each of the Streptomyces species examined by Southern hybridization suggests a common role in morphogenesis in this genus.

An oligoribonuclease gene in Streptomyces griseus

In Streptomyces griseus, A-factor (2-isocapryloyl-3R-hydroxymethyl-gamma-butyrolactone) serves as a microbial hormone that switches on many genes required for streptomycin production and morphological development. An open reading frame (Orf1) showing high sequence similarity to oligoribonucleases of various origins is present just downstream of adpA, one of the A-factor-dependent genes. Orf1 was named OrnA (oligoribonuclease A) because it showed 3'-to-5' exo-oligoribonuclease activity, releasing [(32)P]CMP from ApCpC[(32)P]pC used as a substrate. Reverse transcription-PCR and S1 nuclease mapping analyses revealed that ornA was transcribed from two promoters; one was a developmentally regulated, A-factor-dependent promoter in front of adpA, and the other was a constitutive promoter in front of the ornA coding sequence. Transcription of ornA was thus additively enhanced at the initiation stage for secondary metabolism and aerial mycelium formation. ornA-disrupted strains grew slowly and scarcely formed aerial mycelium. ornA homologues were distributed in a wide variety of Streptomyces species, including S. coelicolor A3(2), as determined by Southern hybridization analysis. Disruption of the ornA homologue in S. coelicolor A3(2) also caused phenotypes similar to those of the S. griseus DeltaornA strains. The OrnA oligoribonucleases in Streptomyces species are therefore not essential but play an important role in vegetative growth and in the initiation of differentiation.

Gene organization for nitric oxide reduction in Alcaligenes faecalis S-6

norB and norC encoding the cytochrome b-containing subunit and the cytochrome c-containing subunit, respectively, of the nitric oxide reductase (NOR) in Alcaligenes faecalis S-6 were cloned and sequenced. Both NorB and NorC showed more than 40% sequence identity to the corresponding subunits of cytochrome bc-type NORs in other denitrifying bacteria. norCB was in a gene cluster containing seven other genes; these were named dnr, orf2, orf3, norE, norF, norQ, and norD on the basis of their similarity with NOR systems in other bacteria. Potential FNR-binding sites were present in front of norCB, norEF, and/or orf2/orf3, suggesting that most of these genes are regulated simultaneously by an FNR-related protein. NorB and NorC proteins produced in the membrane fraction in Escherichia coli showed no enzyme activity, probably due to lack of NorQ and NorD, which appear to perform some essential function for activation of the NorB-NorC complex in the recombinant E. coli.

Characterization of an alg2 mutant of the zygomycete fungus Rhizomucor pusillus

The zygomycete fungus Rhizomucor pusillus secretes an aspartic proteinase (MPP) that contains asparagine ( N )-linked oligosaccharides at two sites. Mutant strain 1116 defective in N -glycosylation secretes MPP with truncated oligo-saccharide chains. Lipid-linked oligosaccharides in mutant 1116 were labeled with [6-(3)H]glucosamine and [2-(3)H]mannose, prepared by cycles of solvent extraction, and analyzed by gel filtration chromatography on a Bio-Gel P-4 column after mild acid-hydrolysis. Mutant 1116 accumulated an intermediate, Man(1)GlcNAc(2)-dolichol pyrophosphate (PP-Dol), whereas wild-type strain F27 synthesized the fully assembled oligosaccharide precursor Glc(3)Man(9)GlcNAc(2)-PP-Dol. Consistent with this, alg2 encoding a mannosyltransferase in the lipid-linked oligosaccharide biosynthetic pathway in mutant 1116 had a 5 bp insertion that generated a stop codon in the middle of the coding sequence. Transformation of mutant 1116 with the intact alg2 gene on a pUC19-derived plasmid generated transformants that contained multicopies of alg2 at the alg2 locus. Glycosylation of the total proteins in the transformants was recovered to the same level as in strain F27, as determined with peroxidase-concanavalin A. These transformants produced MPP mainly with the same N -linked oligosaccharides as that produced by strain F27, but still with truncated oligosaccharides in small amounts. All of these data show that Alg2 is an alpha-1,3 or alpha-1,6 mannosyltransferase that elongates Man(1)GlcNAc(2)-PP-Dol to Man(2)GlcNAc(2)-PP-Dol. The slower growth of mutant 1116 was significantly recovered on introduction of alg2. The viability of the alg2 mutants of the zygomycete R.pusillus makes a contrast with the lethal effect of ALG2 mutations in the yeast Saccharomyces cerevisiae.

The A-factor regulatory cascade leading to streptomycin biosynthesis in Streptomyces griseus : identification of a target gene of the A-factor receptor

In Streptomyces griseus, A-factor (2-isocapryloyl-3R-hydroxymethyl-gamma-butyrolactone) at an extremely low concentration triggers streptomycin biosynthesis and cell differentiation by binding a repressor-type receptor protein (ArpA) and dissociating it from DNA. An A-factor-responsive transcriptional activator (AdpA) able to bind the promoter of strR, a pathway-specific regulatory gene responsible for transcription of other streptomycin biosynthetic genes, was purified to homogeneity and adpA was cloned by PCR on the basis of amino acid sequences of purified AdpA. adpA encoding a 405-amino-acid protein containing a helix-turn-helix DNA-binding motif at the central region showed sequence similarity to transcriptional regulators in the AraC/XylS family. The -35 and -10 regions of the adpA promoter were found to be a target of ArpA; ArpA bound the promoter region in the absence of A-factor and exogenous addition of A-factor to the DNA-ArpA complex immediately released ArpA from the DNA. Consistent with this, S1 nuclease mapping showed that adpA was transcribed only in the presence of A-factor and strR was transcribed only in the presence of intact adpA. Furthermore, adpA disruptants produced no streptomycin and overexpression of adpA caused the wild-type S. griseus strain to produce streptomycin at an earlier growth stage in a larger amount. On the basis of these findings, we propose here a model to demonstrate how A-factor triggers streptomycin biosynthesis at a late exponential growth stage.

Genetic transformation of a Rhizomucor pusillus mutant defective in asparagine-linked glycosylation: production of a milk-clotting enzyme in a less-glycosylated form

Rhizomucor pusillus 1116R3 has a defect in alg2 encoding a mannosyltransferase in the asparagine (N)-linked oligosaccharide biosynthetic pathway and produces proteins in less-glycosylated forms. For development of a genetic transformation system for this zygomycete, an uracil auxotroph (mutant 1116U17) as the host strain was derived by ultraviolet (UV) mutagenesis as 5-fluoroorotic acid-resistant colonies and the orotidine-5'-monophosphate (OMP) decarboxylase (pyr4) gene as a selection marker was cloned from the wild-type strain R. pusillus F27 by the polymerase chain reaction with primers designed on the basis of the pyr4 sequences from other fungi. The amino acid sequence of R. pusillus Pyr4 deduced from the nucleotide sequence showed high homology with the OMP decarboxylases from various fungi. The pyr4 gene on pUC19 (plasmid pRPPyr4) was introduced into protoplasts of R. pusillus 1116U17 by polyethylene glycol-assisted transformation. Transformation under optimized conditions yielded 5 Ura+ transformants with 1 microgram pRPPyr4 DNA and 1 x 10(7) viable protoplasts. Southern blot analysis of the genomic DNA from the transformants showed that multiple copies of the pRPPyr4 sequence were integrated into the genome by homologous recombination at the pyr4 locus. For the purpose of production of a milk-clotting aspartic proteinase (MPP) in a less-glycosylated form, mpp from the wild-type strain was cloned in pRPPyr4 and introduced into protoplasts of R. pusillus 1116U17. Transformants obtained in this way contained multiple copies of mpp at the chromosomal mpp locus and produced MPP as a mixture of molecules having no sugar chains and Man0-1GlcNAc2 at the two N-linked glycosylation sites in an amount about 12 times larger than the parent strain. The transformation system for R. pusillus 1116U17 would be useful for production of proteins with truncated N-linked oligosaccharide chains.

A new pathway for polyketide synthesis in microorganisms

Chalcone synthases, which biosynthesize chalcones (the starting materials for many flavonoids), have been believed to be specific to plants. However, the rppA gene from the Gram-positive, soil-living filamentous bacterium Streptomyces griseus encodes a 372-amino-acid protein that shows significant similarity to chalcone synthases. Several rppA-like genes are known, but their functions and catalytic properties have not been described. Here we show that a homodimer of RppA catalyses polyketide synthesis: it selects malonyl-coenzyme-A as the starter, carries out four successive extensions and releases the resulting pentaketide to cyclize to 1,3,6,8-tetrahydroxynaphthalene (THN). Site-directed mutagenesis revealed that, as in other chalcone synthases, a cysteine residue is essential for enzyme activity. Disruption of the chromosomal rppA gene in S. griseus abolished melanin production in hyphae, resulting in 'albino' mycelium. THN was readily oxidized to form 2,5,7-trihydroxy-1,4-naphthoquinone (flaviolin), which then randomly polymerized to form various coloured compounds. THN formed by RppA appears to be an intermediate in the biosynthetic pathways for not only melanins but also various secondary metabolites containing a naphthoquinone ring. Therefore, RppA is a chalcone-synthase-related synthase that synthesizes polyketides and is found in the Streptomyces and other bacteria.

Leptomycin B inactivates CRM1/exportin 1 by covalent modification at a cysteine residue in the central conserved region

The cellular target of leptomycin B (LMB), a nuclear export inhibitor, has been identified as CRM1 (exportin 1), an evolutionarily conserved receptor for the nuclear export signal of proteins. However, the mechanism by which LMB inhibits CRM1 still remains unclear. CRM1 in a Schizosaccharomyces pombe mutant showing extremely high resistance to LMB had a single amino acid replacement at Cys-529 with Ser. The mutant gene, named crm1-K1, conferred LMB resistance on wild-type S. pombe, and Crm1-K1 no longer bound biotinylated LMB. (1)H NMR analysis showed that LMB bound N-acetyl-L-cysteine methyl ester through a Michael-type addition, consistent with the idea that LMB binds covalently via its alpha, beta-unsaturated delta-lactone to the sulfhydryl group of Cys-529. When HeLa cells were cultured with biotinylated LMB, the only cellular protein bound covalently was CRM1. Inhibition by N-ethylmaleimide (NEM), an alkylating agent, of CRM1-mediated nuclear export probably was caused by covalent binding of the electrophilic structure in NEM to the sulfhydryl group of Cys-529, because the crm1-K1 mutant showed the normal rate for the export of Rev nuclear export signal-bearing proteins in the presence of not only LMB but also NEM. These results show that the single cysteine residue determines LMB sensitivity and is selectively alkylated by LMB, leading to CRM1 inactivation.

Analysis of stability and catalytic properties of two tryptophanases from a thermophile

Two tryptophanases, Tna1 and Tna2, both of which were cloned from the thermophile Symbiobacterium thermophilum, differ in their enzymatic properties, such as thermal stability, catalytic efficiency and activation energy of catalysis, despite the great similarity (92%) in their amino acid sequences. Chimeric tryptophanases were constructed by recombination of the two genes to try to elucidate the molecular basis for the difference. The stability of each chimeric enzyme was roughly proportional to the content of amino acid residues from Tna1. Three regions, tentatively named regions 2, 4 and 5, which contained the amino acid residues 70-129, 192-298 and 299-453, respectively, were especially important for the increase in thermal stability. Site-directed mutagenesis revealed that V104 in region 2 and Y198 in region 4 of Tna1 were involved in the increase in thermal stability of Tna1. Amino acid residues contributing to the higher catalytic efficiency of Tna1 were similarly analyzed, using the chimeric tryptophanases, and found to be located in region 5. Site-directed mutagenesis revealed that I383 and G395 in Tna1, which were presumably located close to the putative active center, played an active role in the increase of catalytic efficiency of Tna1. The activation energy of catalysis was proportional to the content of amino acid residues from Tna2, suggesting the amino acid residues responsible for the difference were dispersed over the whole molecule.

A novel nuclear export signal sensitive to oxidative stress in the fission yeast transcription factor Pap1

Pap1, a fission yeast AP-1-like transcription factor, is negatively regulated by CRM1/exportin 1, the nuclear export factor. Pap1 was localized normally in the cytoplasm but was accumulated in the nucleus when Crm1 was inactivated by a temperature-sensitive mutation or by treatment with leptomycin B, a specific export inhibitor. Deletion of the C-terminal cysteine-rich domain (CRD) resulted in nuclear accumulation of Pap1, while a glutathione S-transferase-green fluorescent protein-CRD fusion protein was localized in the cytoplasm in a Crm1-dependent manner. Deletion and mutational analyses identified several important amino acids in a 19-amino acid region in the CRD as a nuclear export signal (NES). Strikingly, a cysteine residue (Cys-532), in addition to two leucines and an isoleucine, was important for the NES function and the presence of at least one of the two cysteine residues was essential. Unlike classical NESs such as the human immunodeficiency virus Rev NES, the Pap1 NES lost the function upon treatment with oxidants such as diethyl maleate. The oxidative stress response is conserved through evolution, as green fluorescent protein-fused proteins bearing the Pap1 NES expressed in mammalian cells responded to diethyl maleate. These results show that the hydrophobic amino acid-rich region containing two important cysteines in Pap1 serves as a novel NES, which is sensitive to oxidative stress.

Oxamflatin is a novel antitumor compound that inhibits mammalian histone deacetylase

Oxamflatin [(2E)-5-[3-[(phenylsufonyl) aminol phenyl]-pent-2-en-4-ynohydroxamic acid] induces transcriptional activation of junD and morphological reversion in various NIH3T3-derived transformed cell lines. We found that oxamflatin showed in vitro antiproliferative activity against various mouse and human tumor cell lines with drastic changes in the cell morphology and in vivo antitumor activity against B16 melanoma. Oxamflatin caused an elongated cell shape with filamentous protrusions as well as arrest of the cell cycle at the G1 phase in HeLa cells. These phenotypic changes of HeLa cells were apparently similar to those by trichostatin A (TSA), a specific inhibitor of histone deacetylase (HDAC). The effect of oxamflatin on the transcriptional activity of the cytomegalovirus (CMV) promoter was examined and compared with known HDAC inhibitors, TSA, sodium n-butyrate, and FR901228. Oxamflatin as well as all these inhibitors greatly enhanced the transcriptional activity of the CMV promoter in a dose-dependent manner. Oxamflatin, like TSA, inhibited intracellular HDAC activity, as a result of which marked amounts of acetylated histone species accumulated. Finally, effects on expression of several endogenous genes involved in cell morphology and cell cycle control in HeLa cells were analysed. Expression of gelsolin, cyclin E and Cdk inhibitors including p21WAF1/Cip1 was highly augmented, while that of cyclin A and cyclin D1 was decreased by oxamflatin. These results suggest that changes in the expression pattern of the genes regulating cell morphology and the cell cycle due to histone hyperacetylation are responsible for the antitumor activity, the morphological change and the cell cycle arrest induced by oxamflatin.

Neuronal differentiation of neuro 2a cells by inhibitors of cell cycle progression, trichostatin A and butyrolactone I

Trichostatin A (TSA, 17 nM), a specific and reversible inhibitor of histone deacetylase induced neurite network formation at and after 4 days. The networks were preserved for at least 3 weeks in the presence of TSA. Butyrolactone I (BLI, 23.6 microM), an inhibitor of cdc2 and cdk2 kinases, also induced neurite extension. Both compounds enhanced the acetylcholinesterase activity of the cells. Cell cycle progression of the cells was blocked by TSA (17 nM) at G1 phase alone. Furthermore, the level of histone hyperacetylation and p21(WAF1) expression in TSA-treated cells increased transiently. These findings suggest that the induction of the neuronal differentiation in Neuro 2a cells by these agents requires the cell cycle arrest at G1 phase, which is caused by inhibition of cycline dependent kinase, a target molecule of BLI and p21(WAF1).

Trichostatin and leptomycin. Inhibition of histone deacetylation and signal-dependent nuclear export

Trichostatin A (TSA), an inhibitor of the eukaryotic cell cycle and an inducer of morphological reversion of transformed cells, inhibits histone deacetylase (HDAC) at nanomolar concentrations. Recently, trapoxin, oxamflatin, and FR901228, antitumor agents structurally unrelated to TSA, were found to be potent HDAC inhibitors. These inhibitors activate expression of p21Waf1 and 16INK4A in a p53-independent manner. Changes in the expression of these cell cycle regulators by an increase in histone acetylation may be responsible for cell cycle arrest and antitumor activity by HDAC inhibitors. The target molecule of leptomycin B (LMB), a potent antitumor agent, was genetically and biochemically identified as CRM1, a protein reported as being required for chromosome structure control. We showed that CRM1 was a receptor for the nuclear export signal (NES) and that LMB inhibited nuclear export of proteins. Using LMB, we identified a novel NES in fission yeast transcription factor Pap1, the function of which is abolished by oxidative stress in a manner conserved in eukaryotes.

Site-directed mutagenesis of the A-factor receptor protein: Val-41 important for DNA-binding and Trp-119 important for ligand-binding

The A-factor receptor protein (ArpA) plays a key role in the regulation of secondary metabolism and cellular differentiation in Streptomyces griseus. ArpA binds the target DNA site forming a 22 bp palindrome in the absence of A-factor, and exogenous addition of A-factor to the ArpA-DNA complex immediately releases ArpA from the DNA. An amino acid (aa) replacement at Val-41 to Ala in an alpha-helix-turn-alpha-helix (HTH) motif at the N-terminal portion of ArpA abolished DNA-binding activity but not A-factor-binding activity, suggesting the involvement of this HTH in DNA-binding. On the other hand, an aa replacement at Trp-119 to Ala generated a mutant ArpA that was unable to bind A-factor, thus resulting in an A-factor-insensitive mutant that bound normally to its target DNA in both the presence and absence of A-factor. These data suggest that ArpA consisting of two functional domains, one for HTH-type DNA-binding at the N-terminal portion and one for A-factor-binding at the C-terminal portion, is a member of the LacI family. Consistent with this, two ArpA homologues, CprA and CprB, from Streptomyces coelicolor A3(2), each of which contains a very similar aa sequence of the HTH to that of ArpA, also recognized and bound the same DNA target. However, neither CprA nor CprB recognized A-factor, probably due to much less similarity in the C-terminal domains.

Characterization of alg2 encoding a mannosyltransferase in the zygomycete fungus Rhizomucor pusillus

ALG2 of Saccharomyces cerevisiae encodes the glycosyltransferase that mannosylates Man2GlcNAc2-dolichol diphosphate (PP-Dol) and Man1GlcNAc2-PP-Dol to form Man3GlcNAc2-PP-Dol. The genomic DNA and cDNA encoding an ALG2 homologue were cloned from the zygomycete fungus, Rhizomucor pusillus, and their nucleotide sequences were determined. The cloned cDNA under the control of the yeast GAL1 promoter complemented the temperature-sensitive (ts) growth of the alg2-1 mutant of S. cerevisiae, indicating that it represented a functional ALG2 homologue of R. pusillus. Five introns intervened the R. pusillus alg2 encoding a 455-amino-acid (aa) protein that showed end-to-end similarity in aa sequence to yeast Alg2 and contained a dolichol-binding consensus sequence (Val/Ile-x-Phe-x-x-Ile, where x is any aa) very near its C-terminus. The yeast alg2-1 gene had two mutation points at 377Gly to Arg and 386Gln to Lys. alg2-2 also contained two mutations at 54Glu to Lys and 377Gly to Arg. Site-directed mutagenesis of the fungal Alg2 and determination of their phenotypes in the yeast alg2-1 mutant showed that a mutation at 368Gly (equivalent to 377Gly of yeast Alg2) to Arg resulted in generation of a ts enzyme. The fungal Alg2 containing a mutation at the position corresponding to 54Glu or 386Gln of yeast Alg2 still complemented the ts growth of yeast alg2-1.

phd1+, a histone deacetylase gene of Schizosaccharomyces pombe, is required for the meiotic cell cycle and resistance to trichostatin A

A gene named phd1+ encoding a protein highly homologous to the yeast and human histone deacetylases, such as Saccharomyces cerevisiae Rpd3p and human HDAC1, was cloned from Schizosaccharomyces pombe. The immune complex isolated from S. pombe cells expressing Phd1 fused to the FLAG epitope showed histone deacetylase activity, which was inhibited by trichostatin A (TSA), a specific inhibitor of histone deacetylase. The null mutation of phd1+ resulted in a marked decrease in the total cellular histone deacetylase activity and an increase in the sensitivity to TSA. Although the phd1 disruptant showed no obvious defect in the mitotic cell cycle or mating, both homothallic haploid and heterothallic diploid cells failed to form spores in the absence of phd1+. These results indicate that phd1+ encodes a histone deacetylase, which is involved in the meiotic cell cycle in S. pombe.

Characterization of an A-factor-responsive repressor for amfR essential for onset of aerial mycelium formation in Streptomyces griseus

A-factor (2-isocapryloyl-3R-hydroxymethyl-gamma-butyrolactone) is essential for the initiation of aerial mycelium formation in Streptomyces griseus. amfR is one of the genes which, when cloned on a low-copy-number plasmid, suppresses the aerial mycelium-negative phenotype of an A-factor-deficient mutant of S. griseus. Disruption of the chromosomal amfR gene resulted in complete abolition of aerial mycelium formation, indicating that amfR is essential for the onset of morphogenesis. Cloning and nucleotide sequencing of the region upstream of amfR predicted an operon consisting of orf5, orf4, and amfR. Consistent with this idea, Northern blotting and S1 mapping analyses suggested that these three genes were cotranscribed mainly by a promoter (PORF5) in front of orf5. Furthermore, PORF5 was active only in the presence of A-factor, indicating that it is A-factor dependent. Gel mobility shift assays showed the presence of a protein (AdpB) able to bind PORF5 in the cell extract from an A-factor-deficient mutant but not from the wild-type strain. AdpB was purified to homogeneity and found to bind specifically to the region from -72 to -44 bp with respect to the transcriptional start point. Runoff transcriptional analysis of PORF5 with purified AdpB and an RNA polymerase complex isolated from vegetative mycelium showed that AdpB repressed the transcription in a concentration-dependent manner. It is thus apparent that AmfR as a switch for aerial mycelium formation and AdpB as a repressor for amfR are members in the A-factor regulatory cascade, leading to morphogenesis.

Identification of radicicol as an inhibitor of in vivo Ras/Raf interaction with the yeast two-hybrid screening system

Activation of cytoplasmic serine/threonine kinase Raf-1, an important effector of Ras, requires direct binding to Ras. The yeast two-hybrid screening system used for identification of inhibitors of Ras/Raf-1 interaction showed radicicol to be an inhibitor. Radicicol has been shown to induce morphological reversion of transformed cells. Immunoprecipitation with an anti-Ras antibody revealed that the in vivo Ras/Raf-1 binding in v-Ha-ras-transformed cells was also blocked by low concentrations of radicicol (0.1 approximately 1 microg/ml), while degradation of Raf-1 was induced at concentrations higher than 2 microg/ml. However, in vitro binding of glutathion S-transferase-fused Ras to a maltose binding protein-fused RIP3 containing the Ras-binding domain (RBD) of Raf-1 was not inhibited by radicicol. Similar two-hybrid assays with several truncated forms of Raf-1 showed that both the conserved serine/threonine-rich domain (CR2) and the C-terminal protein kinase domain (CR3) were required for the full inhibition by radicicol. These results suggest that radicicol interacts directly or indirectly with the region except with RBD of Raf-1, thereby inhibiting a conformational change of Raf-1 prerequisite for binding to Ras.

Production of trehalose synthase from a basidiomycete, Grifola frondosa, in Escherichia coli

The genomic DNA and cDNA for a gene encoding a novel trehalose synthase (TSase) catalyzing trehalose synthesis from alpha-D-glucose 1-phosphate and D-glucose were cloned from a basidiomycete, Grifola frondosa. Nucleotide sequencing showed that the 732-amino-acid TSase-encoding region was separated by eight introns. Consistent with the novelty of TSase, there were no homologous proteins registered in the data-bases. Recombinant TSase with a histidine tag at the NH2-terminal end, produced in Escherichia coli, showed enzyme activity similar to that purified from the original G. frondosa strain. Incubation of alpha-D-glucose 1-phosphate and D-glucose in the presence of recombinant TSase generated trehalose, in agreement with the enzymatic property of TSase that the equilibrium lay far in the direction of trehalose synthesis.

Leptomycin B inhibition of signal-mediated nuclear export by direct binding to CRM1

Leptomycin B (LMB) is a Streptomyces metabolite that inhibits nuclear export of the human immunodeficiency virus type 1 regulatory protein Rev at low nanomolar concentrations. Recently, LMB was shown to inhibit the function of CRM1, a receptor for the nuclear export signal (NES). Here we show evidence that LMB binds directly to CRM1 and that CRM1 is essential for NES-dependent nuclear export of proteins in both yeast and mammalian cells. Binding experiments with a biotinylated derivative of LMB and a HeLa cell extract led to identifying CRM1 as a major protein that bound to the LMB derivative. Microinjection of a purified anti-human CRM1 antibody into the mammalian nucleus specifically inhibited nuclear export of NES-containing proteins, as did LMB. Consistent with this, CRM1 was found to interact with NES, when assayed with immobilized NES and HeLa cell extracts. This association was disrupted by adding LMB or purified anti-human CRM1 antibody. The inhibition of CRM1 by LMB was also observed in fission yeast. The fission yeast crm1 mutant was defective in the nuclear export of NES-fused proteins, but not in the import of nuclear localization signal (NLS)-fused proteins. Interestingly, a protein containing both NES and NLS, which is expected to shuttle between nucleus and cytoplasm, was highly accumulated in the nucleus of the crm1 mutant cells or of cells treated with LMB. These results strongly suggest that CRM1 is the target of LMB and is an essential factor for nuclear export of proteins in eukaryotes.