The Ser36-Ser37 pair in HeLa nuclear protein p21/SIIR mediates Ser/Thr phosphorylation and is essential for Rous sarcoma virus long terminal repeat repression

Phosphorylation of HeLa SII (or TFIIS)-related nuclear protein p21/SIIR was demonstrated in transfected COS-1 cells. To test for a possible functional link between phosphorylation and the previously described Rous sarcoma virus (RSV) long terminal repeat (LTR) repression (Yeh, C.H., and Shatkin, A.J. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 11002-11006), p21/SIIR mutants were constructed and assayed for phosphorylation level and effect on RSV LTR-driven chloramphenicol acetyltransferase (CAT) reporter expression. A major phosphorylation target in p21/SIIR was localized to the Arg/Ser-rich region between amino acids 12 and 49. Deletion of this region impaired the ability of p21/SIIR to down-regulate RSV LTR promoter function. Four serine pairs, all displaying the Arg/Lys-Ser-Ser motif typical of phosphorylation sites, are present in p21/SIIR between positions 31 and 48. Conversion of these individual serine pairs to alanine resulted in decreased phosphorylation in each case. Mutation of the Ser36-Ser37 pair also diminished by severalfold the repression activity of p21/SIIR. The single tyrosine (Tyr155) in p21/SIIR was not detectably phosphorylated in transfected COS-1 cells, suggesting that the Ser36-Ser37 pair mediates Ser/Thr phosphorylation of p21/SIIR and is critical for LTR repression function.

A recombinant rice 16.9-kDa heat shock protein can provide thermoprotection in vitro

It is difficult to obtain large amounts of purified low-molecular-mass heat shock proteins (LMM HSPs), which are unique to plants, for biochemical and physiological studies. Therefore, an attempt was made to produce such a HSP by applying recombinant DNA technology. We fused the cDNA for a rice class I 16.9-kDa HSP, pTS1, to the gene for glutathione S-transferase (GST) of Schistosoma japonicum and we obtained large amounts of the fusion protein from transformed Escherichia coli cells. In addition, we found that the 16.9-kDa HSP obtained by cleavage of the recombinant protein could also form a protein complex of approximately 310 kDa under nondenaturing conditions as can the small, native, class I HSPs from heat-shocked rice seedlings. An assay in vitro to examine the thermoprotection of rice soluble proteins from heat denaturation revealed the strong stabilizing effect of the recombinant HSP.

A cis-acting element in Rous sarcoma virus long terminal repeat required for promoter repression by HeLa nuclear protein p21

HeLa cell basic nuclear protein (p21), which represses Rous sarcoma virus long terminal repeat (RSV LTR) promoter activity, diminished v-src expression and the appearance at permissive temperature of the transformed phenotype in tsRSVLA23 Rat-1, a cell line transformed with a temperature-sensitive mutant of RSV. Nuclear run-on analyses using COS-1 cells cotransfected with p21 cDNA and chloramphenicol acetyltransferase reporter indicated that p21 inhibits transcription initiation by targeting a region in the RSV LTR promoter between positions -108 and -85 upstream of the cap site. Insertion of this 24-base pair sequence in place of one of the 72-base pair enhancers in the SV40 early promoter rendered it sensitive to p21 repression. Electrophoretic mobility shift assays using a synthetic oligomer corresponding to the 24-base pair LTR promoter element revealed that p21 altered the pattern of protein.DNA complex formation apparently without binding DNA directly. Complex formation assayed by UV cross-linking and DNA affinity chromatography indicated further that a cellular factor which can interact with this element was decreased in cells transfected with p21 expression plasmid. The results indicate that p21 repression of RSV LTR is mediated by a cis-acting element and may occur by alteration of protein complexes formed on this promoter element.

Down-regulation of Rous sarcoma virus long terminal repeat promoter activity by a HeLa cell basic protein

We have previously isolated a HeLa cell cDNA encoding a 21-kDa polypeptide that is 48% similar to transcription factor IIS. To explore the possibility that p21 plays a role in transcriptional regulation in vivo, we tested the effect of p21 expression on the synthesis of reporter chloramphenicol acetyltransferase (CAT) in transfected COS-1 cells. CAT formation under control of the Rous sarcoma virus long terminal repeat (RSV LTR) promoter was decreased nearly 20-fold in cells coexpressing p21. In contrast, CAT production under control of other sequence elements was only slightly reduced (human immunodeficiency virus type 1 LTR, simian virus 40 early promoter), unaffected (human heat shock protein of 70-kDa promoter, adenovirus major late promoter TATA box), or increased (terminal deoxynucleotidyltransferase initiator element, c-fos promoter) by p21 coexpression as compared to cells cotransfected with the parental vector. The abundance of steady-state CAT transcripts from RSV LTR was also decreased by p21 expression in a dose-dependent manner, suggesting that transcription of RSV LTR/CAT is under negative control by p21. Consistent with an effect on transcription, p21 was localized in nuclei of transfected cells. Deletion analysis of p21 indicated that the sequences essential for inhibition of RSV LTR function include the previously identified ARg/Ser-rich region and zinc finger-like motif. Proliferation of chicken embryo fibroblasts transfected with an infectious molecular clone of RSV was diminished by p21 expression, which also resulted in fewer transformed foci.

Mouse liver NAD(P)H:quinone acceptor oxidoreductase: protein sequence analysis by tandem mass spectrometry, cDNA cloning, expression in Escherichia coli, and enzyme activity analysis

The amino acid sequence of mouse liver NAD(P)H:quinone acceptor oxidoreductase (EC 1.6.99.2) has been determined by tandem mass spectrometry and deduced from the nucleotide sequence of the cDNA encoding for the enzyme. The electrospray mass spectral analyses revealed, as previously reported (Prochaska HJ, Talalay P, 1986, J Biol Chem 261:1372-1378), that the 2 forms--the hydrophilic and hydrophobic forms--of the mouse liver quinone reductase have the same molecular weight. No amino acid sequence differences were found by tandem mass spectral analyses of tryptic peptides of the 2 forms. Moreover, the amino-termini of the mouse enzymes are acetylated as determined by tandem mass spectrometry. Further, only 1 cDNA species encoding for the quinone reductase was found. These results suggest that the 2 forms of the mouse quinone reductase have the same primary sequences, and that any difference between the 2 forms may be attributed to a labile posttranslational modification. Analysis of the mouse quinone reductase cDNA revealed that the enzyme is 273 amino acids long and has a sequence homologous to those of rat and human quinone reductases. In this study, the mouse quinone reductase cDNA was also ligated into a prokaryotic expression plasmid pKK233.2, and the constructed plasmid was used to transform Escherichia coli strain JM109. The E. coli-expressed mouse quinone reductase was purified and characterized. Although mouse quinone reductase has an amino acid sequence similar to those of the rat and human enzymes, the mouse enzyme has a higher NAD(P)H-menadione reductase activity and is less sensitive to flavones and dicoumarol, 2 known inhibitors of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

A HeLa-cell-encoded p21 is homologous to transcription elongation factor SII

A 1.2-kb cDNA clone isolated from a HeLa cell library contains an open reading frame encoding a new protein (p21) of 21 kDa that is approx. 48% similar to members of the eukaryotic transcription elongation factor SII (TFIIS) family. The deduced amino-acid sequence of p21 indicates that it is hydrophilic, basic and contains nuclear localization signals, as well as multiple consensus phosphorylation sites.

Expression and biochemical characterization of human glucose-6-phosphate dehydrogenase in Escherichia coli: a system to analyze normal and mutant enzymes

We have developed a system to characterize normal and mutated glucose-6-phosphate dehydrogenase (G6PD) enzymes in vitro. Normal or mutant G6PD cDNA was subcloned into a pGEX-3X vector, which allowed production of a functional fusion protein in Escherichia coli. When we compared the recombinant normal enzyme with authentic human G6PD, indistinguishable Km values for glucose-6-phosphate (G6P) and NADP were obtained, and the utilization rates for two substrate analogues (2-deoxy G6P and deamino NADP) also showed no difference between the enzymes. This system was used to assay a biochemically uncharacterized variant, G6PD Taipei (493 A-->G; 165 Asn-->Asp), plus two other known mutations (487 G-->A; 163 Gly-->Ser and 592 C-->T; 198 Arg-->Cys) that are located close to or within the putative G6P binding domain. Our results show that the G6PD activities of these three mutants were greatly reduced. No significant alteration in G6PD kinetics was observed for both 487 and 493 mutations. However, a drastic reduction in the Km for G6P (4-fold decrease) and tremendous increases in utilization rates of 2-deoxy G6P (32-fold increase) and deamino NADP (6-fold increase) were associated with the 592 mutation. This results suggests that arginine 198 in human G6PD, possibly located within the putative G6P binding domain, may play an important role in binding the substrate G6P. In addition, we and others have recently identified that at least nine different types of mutations are responsible for G6PD deficiency in Chinese. In this report, we also present the occurrence rate of each mutation present in the population of Taiwan.

Plant low-molecular-mass heat-shock proteins: their relationship to the acquisition of thermotolerance in plants

Among the heat-shock proteins (HSPs) induced in response to heat-shock (HS) in all organisms, the low-molecular-mass (LMM) HSPs are the most abundant and unique in plants. The HSP genes at the transcriptional and the translational levels have been well-characterized; however, relatively little is known about the physiological function of HSPs. We have been studying the biological role of plant LMM HSPs based on the suggestion by Minton, Karmin, Hahn and Minton ([1982] Proc. Natl. Acad. Aci. U.S.A. 79, 7107-711) that HSPs may act as heat-stable proteins to non-specifically stabilize other proteins which are highly susceptible to inactivation or denaturation by heat. For the future, LMM-HSP gene transfer into organisms that do not synthesize plant LMM HSPs would be a way of determining the function of LMM HSPs, and success could be of practical importance.

Microsequence and mass spectral analysis of nonspecific cross-reacting antigen 160, a CD15-positive neutrophil membrane glycoprotein. Demonstration of identity with biliary glycoprotein

Sequence information was obtained from low picomole amounts of nonspecific cross-reacting antigen (NCA) 160 (M(r) 160,000), a granulocyte membrane glycoprotein. Following affinity purification and SDS-polyacrylamide gel electrophoresis, the protein was electrotransferred to nitrocellulose, digested with trypsin, and the peptides were isolated using capillary reversed-phase liquid chromatography. Analysis of these peptides by Edman microsequencing and mass spectrometry established that NCA-160 was identical to biliary glycoprotein I, a protein that we previously cloned from a human colon library (1). NCA-160 from human granulocytes is a CD15-positive glycoprotein belonging to the carcinoembryonic antigen family and possesses putative transmembrane and cytoplasmic domains. Previous efforts to characterize this antigen at the protein level were hampered by a blocked NH2 terminus. In this study, we confirmed 20% of the deduced amino acid sequence starting with approximately 50 pmol of sample. Carbohydrate structural data is also presented on a single N-linked oligosaccharide moiety located in the A' domain. The capillary high performance liquid chromatography techniques used here, as well as mass spectrometry, were essential for high sensitivity analysis of the blotted, digested glycoprotein.

Aplysia peptide neurotransmitters beta-bag cell peptide, Phe-Met-Arg-Phe-amide, and small cardioexcitatory peptide B are rapidly degraded by a leucine aminopeptidase-like activity in hemolymph

We have been investigating the role of proteolytic enzymes in the inactivation of peptide neurotransmitters in the marine snail Aplysia. Previous studies (Squire, C. R., Talebian, M., Menon, J. G., Dekruyff, S. D., Lee, T. D., Shively, J. E., and Rothman, B. S. (1991) J. Biol. Chem. 266, 22355-22363) showed that neuroactive fragments of the neurotransmitter alpha-bag cell peptide (alpha-BCP) were rapidly degraded (t1/2 = 0.5-2.7 min) in plasma, hemolymph that had been cleared by centrifugation. Degradation was caused by one or more enzymes resembling mammalian leucine amino-peptidase (LAP, EC 3.4.11.1). In this report we show that three other Aplysia peptide neurotransmitters, beta-BCP(1-5) (Arg-Leu-Arg-Phe-His), FMRFa (Phe-Met-Arg-Phe-amide), and SCPB(1-9) (Met-Asn-Tyr-Leu-Ala-Phe-Pro-Arg-Met-amide) are rapidly degraded (t1/2 = 0.3-2.4 min) in plasma by apparently the same LAP-like enzyme(s). Our findings strongly suggest that the LAP-like enzyme(s), by means of its broad substrate specificity and access to the extracellular spaces of the nervous system in vivo, plays a significant role in the inactivation of many Aplysia peptide neurotransmitters, and they raise the possibility that proteolytic enzymes in the extracellular fluid contribute significantly to the inactivation of peptide neurotransmitters in other animal species.

Interleukin-6 is released in the cutaneous response to allergen challenge in atopic individuals

The mechanisms responsible for cutaneous response to antigen are complex. Interleukin-1 (IL-1) and interleukin-6 (IL-6) are proinflammatory cytokines that share many properties. Previous studies with a blister-chamber model have demonstrated IL-1 to be produced in the cutaneous response to antigen. Since IL-2 production by activated T cells and IL-6 production by macrophages are both stimulated by IL-1, we hypothesized that IL-2 and IL-6 may be involved in the cutaneous late-phase response (LPR) to antigen. We examined antigen-challenged sites for IL-2 immunoreactivity (ELISA) but found no difference between antigen- and diluent-challenged skin sites (N = 4). Since IL-2 has been demonstrated to be produced in response to IL-1 and IL-1 activity has been demonstrated to be greatest between hours 10 and 12, we speculated that IL-2 might not be detected until after hour 12. We were unable to demonstrate any increase in IL-2 production, even by extending our studies to 24 hours in two subjects. Antigen-challenged, skin blister-chamber fluids from atopic subjects demonstrated the appearance of IL-6 (ELISA) in pooled samples representing hours 1 1/2, 3 1/2, 5 1/2, and 7, but not at diluent control sites (p less than 0.05; N = 6). IL-6 reached a median peak of 0.66 ng/ml at 3 1/2 hours. Median levels of IL-6 fell to baseline at 8 hours, followed by a second peak of 0.25 ng/ml at hour 10. Three distinct patterns of IL-6 release were noted: early release of IL-6 followed by a sustained slower rise that peaked at hour 9 before declining to baseline levels at 12 hours, early release of IL-6 followed by a fall to baseline levels at hours 7 to 9 with a second smaller peak at hours 9 to 11, and isolated early release of IL-6. Early IL-6 production correlated with late histamine production (R = 0.801; p = 0.06), and late IL-6 production correlated with eosinophil influx (R = 0.813; p = 0.05). The area of the LPR at skin test sites correlated with early IL-6 peak levels (R = 0.977; p = 0.004) and with total early IL-6 production (R = 0.885; p = 0.05), but not with late IL-6 production.(ABSTRACT TRUNCATED AT 400 WORDS)

Diverse point mutations result in glucose-6-phosphate dehydrogenase (G6PD) polymorphism in Taiwan

Glucose-6-PHOSPHATE dehydrogenase (G6PD; EC 1.1.1.49) deficiency is the most common human enzymopathy, affecting more than 200 million people worldwide. Although greater than 400 variants have been described based on clinical and biochemical criteria, little is known about the molecular basis of these G6PD deficiencies. Recently, the gene that encodes human G6PD has been cloned and sequenced, which enables us to examine directly the heterogeneity of G6PD at the DNA level. During the past 10 years, we examined the G6PD activity in 21,271 newborn Chinese infants (11,400 males and 9,871 females) and identified 314 (2.8%) males and 246 (2.5%) females having low G6PD activity. The G6PD gene from 10 randomly selected affected individuals and their relatives was polymerase chain reaction (PCR) amplified, subcloned, and sequenced. Our results indicate that at least four types of mutation are responsible for the G6PD polymorphism in Taiwan. The first type of mutation (487 G----A) was found in an affected Chinese with a G to A change at nucleotide 487, which results in a (163)Gly to Ser substitution. The second type of mutation (493 A----G) is a novel mutation that has not been reported in any other ethnic group and was identified in two affected Chinese. This mutation causes an A to G change at nucleotide position 493, producing an (165)Asn to Asp substitution. Interestingly, the 487 G----A and 493 A----G mutations create Alu I and Ava II recognition sites, respectively, which enabled us to rapidly detect these two mutations by PCR/restriction enzyme (RE) digestion method. The third mutation (1376 G----T) was found in four affected Chinese. This mutation causes a G to T change at nucleotide position 1376 that results in an (459)Arg to Leu substitution. The 1376 G----T mutation seems to be the dominant allele that causes G6PD deficiency in Taiwan. Finally, two affected Chinese were identified as having the fourth mutation (1388 G----A). This mutation causes a G to A change at nucleotide 1388 that produces an (463)Arg to His substitution. Our studies provide the direct proof of the genetic heterogeneity of G6PD deficiency in the Chinese populations of Taiwan and the PCR/RE digestion method is suitable for simultaneous detection of the 487 G----A and 493 A----G mutations.

Purification and characterization of platelet factor XI

Factor XI activity and antigen was purified about 300 fold from human platelets through chromatography on Con-A Sepharose, SP-Sephadex C-50, immobilized goat anti-factor XI, and SP-Sephadex. The partially purified platelet factor XI (Pt-XI) could be activated by activated factor XII generated in situ from single chain factor XI in a reaction requiring high molecular weight kininogen (HMWK) and a surface. Native Pt-XI migrated as a molecule of Mr = 245,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) as identified by Western blotting. On reduction, Pt-XI appeared to have a Mr = 52,000. Neither form was affected by exposure to trypsin. Incubation of Pt-XI with purified factor XII, HMWK, and kaolin produced activated platelet factor XI clotting activity and, concomitantly, the generation over time of a new chain on reduced SDS-PAGE of Mr = 44,500. The coagulant activity of the activated form could be neutralized by diisopropyl flurophosphate (DFP). Incubation of the activated mixture with 3H-DFP followed by reduced SDS-PAGE showed the active site to be associated with a unit of Mr = 44,500. The adsorption domain as defined by adsorption to kaolin was localized to the Mr = 44,500 chain containing the active site. Hence, both active site and adsorption functions, properties of separate chains in plasma factor XI, reside in the same chain of Mr = 44,500 of platelet factor XI.

Nuclear magnetic resonance relaxation studies of the interaction of ligands with the monomer and tetramer forms of formyltetrahydrofolate synthetase

Previous work using n.m.r. spectroscopy to investigate the binding between formyltetrahydrofolate synthetase and its ligands was done using the catalytically active tetrameric form of the enzyme. By removal of specific monovalent cations the tetramer dissociates to four identical, catalytically inactive monomers, which are capable of binding nucleotides with affinities similar to those obtained with the tetramer. In the studies reported here, we examined the interaction of metal-nucleotide, formate and monovalent cations with the monomer using n.m.r. relaxation measurements. We were able to demonstrate that formate binds to the monomer. The spin-lattice relaxation rate (1/T1) of the formate carbon in the monomer.M2+.ADP.formate complex is enhanced when Mg2+ is replaced by Mn2+. By assuming that the exchange of formate is not rate-limiting and that tau c of the monomer is the same as that of the tetramer, the distance between the Mn2+ and the formate carbon was calculated and found to be similar in the monomer and tetramer complexes. The spin-lattice relaxation rates of [13C]trimethylammonium ion (an inactive monovalent cation), [13C]methylammonium and [15N]ammonium ions (both active monovalent cations), were measured in the presence of tetramer, MnADP and formate. The relaxation rates of methylammonium and ammonium ions were enhanced under these conditions whereas the relaxation rate of trimethylammonium ion was not. The results indicate that the active monovalent cations bind near the MnADP binding site. A distance from the Mn2+ to the ammonium nitrogen of between 0.5 and 0.6 nm was calculated.