Extreme cold sensitivity of Salmonella typhimurium umu clones, effects of the umu region and flanking sequences

The umuDC operons of both Salmonella typhimurium and Escherichia coli encode proteins which are essential for mutagenesis following exposure to ultraviolet radiation or a variety of chemicals. However S. typhimurium is less mutable and its umu operon appears to be less active for reasons that are unknown. This study shows that pBR322-based plasmids carrying cloned umuDC operons of either species confer cold sensitivity on both an E. coli umuC strain and a S. typhimurium pSLT- strain. Both S. typhimurium and E. coli umu clones make these lexA+ strains moderately cold-sensitive, but sensitivity produced by the cloned S. typhimurium umuDC operon is extreme when flanking regions of the chromosome are also present. Such instability might be significant in terms of explaining the polymorphisms seen in the regions of the chromosomes of Enterobacteriaceae surrounding the umuDC operon. In S. typhimurium this extreme cold sensitivity was almost certainly responsible for the delayed recognition of a chromosomal umuDC operon.

Activation of Bacillus subtilis transcription factor sigma B by a regulatory pathway responsive to stationary-phase signals

Alternative transcription factor sigma B of Bacillus subtilis controls a stationary-phase regulon induced under growth conditions that do not favor sporulation. Little is known about the metabolic signals and protein factors regulating the activity of sigma B. The operon containing the sigma B structural gene has the gene order orfV-orfW-sigB-rsbX, and operon expression is autoregulated positively by sigma B and negatively by the rsbX product (rsbX = regulator of sigma B). To establish the roles of the orfV and orfW products, orfV and orfW null and missense mutations were constructed and tested for their effects on expression of the sigma B-dependent genes ctc and csbA. These mutations were tested in two contexts: in the first, the sigB operon was under control of its wild-type, sigma B-dependent promoter, and in the second, the sigB operon promoter was replaced by the inducible Pspac promoter. The principal findings are that (i) the orfV (now called rsbV) product is a positive regulator of sigma B-dependent gene expression; (ii) the orfW (now called rsbW) product is a negative regultor of such expression; (iii) sigma B is inactive during logarithmic growth unless the rsbW product is absent; (iv) the rsbX, rsbV, and rsbW products have a hierarchical order of action; and (v) both the rsbV and rsbW products appear to regulate sigma B activity posttranslationally. There are likely to be at least two routes by which information can enter the system to regulate sigma B: via the rsbX product, and via the rsbV and rsbW products.

Effects of SH2 and SH3 deletions on the functional activities of wild-type and transforming variants of c-Src

The amino-termina, noncatalytic half of Src contains two domains, designated the Src homology 2 (SH2) and Src homology 3 (SH3) domains, that are highly conserved among members of the Src family of tyrosine kinases. The SH2 domain (which can be further divided into the B and C homology boxes) and the SH3 domain (also referred to as the A box) are also found in several proteins otherwise unrelated to protein tyrosine kinases. It is believed that these domains are important for directing specific protein-protein interactions necessary for the proper functioning of Src. To determine the importance of the SH2 and SH3 domains in regulating the functions of c-Src, we evaluated mutants of c-Src lacking the A box (residues 88 to 137), the B box (residues 148 to 187) or the C box (residues 220 to 231). Each of these deletions caused a 14- to 30-fold increase in the in vitro level of kinase activity of c-Src. Chicken embryo fibroblasts expressing the deletion mutants displayed a transformed cell morphology, formed colonies in soft agar, and contained elevated levels of cellular phosphotyrosine-containing proteins. Src substrates p36, p85, p120, p125, the GTPase-activating protein (GAP), and several GAP-associated proteins were phosphorylated on tyrosine in cells expressing the A, B, or C box deletion mutant. p110 was highly phosphorylated in cells expressing the C box mutant, was weakly phosphorylated in cells expressing the B box mutant, and was not phosphorylated in cells expressing the A box mutant. Expression of the mutant proteins caused a reorganization of the actin cytoskeleton similar to that seen in v-Src-transformed cells. In addition, deletion of the A, B, or C box did not diminish the transforming or enzymatic activity of an activated variant of c-Src, E378G. These data indicate that deletion of the A, B, or C homology box causes an activation of the catalytic and transforming potential of c-Src and that while these mutations caused subtle differences in substrate phosphorylation, the homology boxes are not required for many of the phenotypic changes associated with transformation by Src.

Ras is essential for nerve growth factor- and phorbol ester-induced tyrosine phosphorylation of MAP kinases

Treatment of PC12 cells with nerve growth factor (NGF) induces a rapid increase in tyrosine phosphorylation of multiple cellular proteins. Expression of a dominant inhibitory Ras mutant specifically blocked NGF- and TPA-induced tyrosine phosphorylation of two proteins of approximately 42 and 44 kd. Conversely, expression of an oncogenic variant of Ras induced tyrosine phosphorylation of the same 42 and 44 kd proteins. The 44 kd protein was immunoprecipitated with an antibody directed against extracellular signal-regulated kinase 1/mitogen-activated protein kinase (MAPK) and the 42 kd protein comigrated with a 42 kd MAPK, indicating that at least one and probably both Ras-regulated phosphoproteins are MAPKs. In addition, MAPK activation, as measured by in vitro phosphorylation of myelin basic protein, was also regulated by Ras. Ras was not required for NGF-induced activation of Trk or tyrosine phosphorylation of PLC-gamma 1. Thus, NGF-induced tyrosine phosphorylation occurs both prior to and following Ras action, and Ras plays a critical role in the NGF- and TPA-induced tyrosine phosphorylation of MAPKs.

Signal transduction by nerve growth factor and fibroblast growth factor in PC12 cells requires a sequence of src and ras actions

We have investigated the roles of pp60c-src and p21c-ras proteins in transducing the nerve growth factor (NGF) and fibroblast growth factor (FGF) signals which promote the sympathetic neuronlike phenotype in PC12 cells. Neutralizing antibodies directed against either Src or Ras proteins were microinjected into fused PC12 cells. Each antibody both prevented and reversed NGF- or FGF-induced neurite growth, a prominent morphological marker for the neuronal phenotype. These data demonstrate the involvement of both pp60c-src and p21c-ras proteins in NGF and FGF actions in PC12 cells, and establish a physiological role for the pp60c-src tyrosine kinase in signal transduction pathways initiated by receptor tyrosine kinases in these cells. Additional microinjection experiments, using PC12 transfectants containing inducible v-src or ras oncogene activities, demonstrated a specific sequence of Src and Ras actions. Microinjection of anti-Ras antibody blocked v-src-induced neurite growth, but microinjection of anti-Src antibodies had no effect on ras oncogene-induced neurite growth. We propose that a cascade of Src and Ras actions, with Src acting first, is a significant feature of the signal transduction pathways for NGF and FGF. The Src-Ras cascade may define a functional cassette in the signal transduction pathways used by growth factors and other ligands whose receptors have diverse structures and whose range of actions on various cell types include mitogenesis and differentiation.

Leukemia inhibitory factor and interleukin-6 trigger the same immediate early response, including tyrosine phosphorylation, upon induction of myeloid leukemia differentiation

Leukemia inhibitory factor (LIF) and interleukin-6 (IL-6), two multifunctional cytokines lacking structural homology and binding to distinct receptors, share interesting functional similarities, which include induction of hematopoietic differentiation in normal and myeloid leukemia cells, induction of neuronal cell differentiation, and stimulation of acute-phase protein synthesis in hepatocytes. Structural information on the LIF receptor is not yet available, whereas recent cloning of the IL-6 receptor has shown it to be bipartite, with a signal-transducing subunit that lacks sequence homology to known protein kinases and produces second messengers of unknown nature. The molecular nature of the mechanisms which LIF and IL-6 use to induce cell differentiation is not known. To address this issue, we took advantage of a clone of M1 myeloblastic leukemia cells capable of being induced for terminal differentiation by both LIF and IL-6 directly activate the same set of immediate early response genes upon induction of M1 myeloid differentiation. At least two mechanisms of gene activation, one transcriptional and the other posttranscriptional, are shown to be involved. It is also shown that the LIF and IL-6 immediate early response, at suboptimal cytokine concentrations, is additive. Using a variety of protein kinase activators and inhibitors, we have shown that the intracellular signalling pathways for both LIF and IL-6 are distinct from those of known second messengers and involve protein phosphorylation, notably tyrosine phosphorylation of a 160-kDa protein, as an essential step(s) in the immediate early activation of MyD gene expression. These observations indicate that the functional similarities of LIF and IL-6 as inducers of cell differentiation prevail at the level of the complex differentiation immediate early response and implicate common mechanisms of signal transduction for LIF- and IL-6-induced differentiation.

Induction of neurite outgrowth by v-src mimics critical aspects of nerve growth factor-induced differentiation

PC12 cells treated with nerve growth factor (NGF) or infected with Rous sarcoma virus differentiate into sympathetic, neuronlike cells. To compare the differentiation programs induced by NGF and v-src, we have established a PC12 cell line expressing a temperature-sensitive v-src protein. The v-src-expressing PC12 cell line was shown to elaborate neuritic processes in a temperature-inducible manner, indicating that the differentiation process was dependent on the activity of the v-src protein. Further characterization of this cell line, in comparison with NGF-treated PC12 cells, indicated that the events associated with neurite outgrowth induced by these two agents shared features but could be distinguished by others. Both NGF- and v-src-induced neurite outgrowths were reversible. In addition, NGF and v-src could prime PC12 cells for NGF-induced neurite outgrowth, and representative early and late NGF-responsive genes were also induced by v-src. However, unlike NGF-induced neurite growth, v-src-induced neurite outgrowth was not blocked at high cell density. A comparison of phosphotyrosine containing-protein profiles showed that v-src and NGF each increase tyrosine phosphorylation of multiple cellular proteins. There was overlap in substrates; however, both NGF-specific and v-src-specific tyrosine phosphorylations were observed. One protein which was found to be phosphorylated in both the NGF- and v-src-induced PC12 cells was phospholipase C-gamma 1. Taken together, these results suggest that v-src's ability to function as an inducing agent may be a consequence of its ability to mimic critical aspects of the NGF differentiation program and raise the possibility that Src-like tyrosine kinases are involved in mediating some of the events triggered by NGF.

Different mechanisms for SOS induced alleviation of DNA restriction in Escherichia coli

The alleviation of DNA restriction during the SOS response in Escherichia coli has been further investigated. With the EcoK DNA restriction system UV irradiated wild-type cells show a 10(4)-fold increase in ability to plate non-modified lambda phage and a 3-4 fold increase in transformation by non-modified plasmid DNA. A role for the umuDC genes of E coli in the process of SOS-induced restriction alleviation was identified by showing that a umuC122::Tn5 mutant could alleviate EcoK restriction to only 5% that of wild-type levels. Although umuDC are better characterized for their pivotal role in SOS induced mutagenesis, it is demonstrated here that umu-dependent alleviation of EcoK restriction is a transient process in which umu-dependent mutagenesis plays little part. A second form of SOS induced alleviation of DNA restriction is described in this paper involving the McrA restriction system. The mcrA gene is shown to be encoded within a defective prophage called e14 situated at the 25 min region on the Escherichia coli genetic map. e14 is known to abortively excise from the chromosome after SOS induction and it is demonstrated in this report that mcrA is lost from the genome after SOS induction as part of e14. This results in co-ordinate decrease in the level of McrA restriction within a population of cells.

Assessment of attitudes toward school-based health promotion programs

Teachers from Orleans Parish public junior and senior high schools completed a survey designed to assess their health-related behaviors and their attitudes toward school-based health promotion programs. Findings suggest that teachers' behaviors and attitudes, as well as school policies toward smoking, are not optimal to creating a pro-health promotion environment. While teachers recognize the value of preventive programs for adolescents and many feel well qualified to implement such programs, few actually do. Resolution of these discrepancies are necessary early steps in increasing primary efforts needed for cancer control in Louisiana.

Similar organization of the sigB and spoIIA operons encoding alternate sigma factors of Bacillus subtilis RNA polymerase

Bacillus subtilis sigma-B is an alternate sigma factor implicated in controlling stationary-phase gene expression. We characterized the genetic organization and regulation of the region containing the sigma-B structural gene (sigB) to learn which metabolic signals and protein factors govern sigma-B function. sigB lay in an operon with four open reading frames (orfs) in the order orfV-orfW-sigB-orfX, and lacZ gene fusions showed that all four frames were translated in vivo. Experiments with primer extension, S1 nuclease mapping, and lacZ transcriptional fusions found that sigB operon transcription initiated early in stationary phase from a site 32 nucleotides upstream of orfV and terminated 34 nucleotides downstream of orfX. Fusion expression was abolished in a strain carrying an in-frame deletion in sigB, suggesting that sigma-B positively regulated its own synthesis, and deletions in the sigB promoter region showed that sequences identical to the sigma-B-dependent ctc promoter were essential for promoter activity. Fusion expression was greatly enhanced in a strain carrying an insertion mutation in orfX, suggesting that the 22-kilodalton (kDa) orfX product was a negative effector of sigma-B expression or activity. Notably, the genetic organization of the sigB operon was strikingly similar to that of the B. subtilis spoIIA operon, which has the gene order spoIIAA-spoIIAB-spoIIAC, with spoIIAC encoding the sporulation-essential sigma-F. The predicted sequence of the 12-kDa orfV product was 32% identical to that of the 13-kDa SpoIIAA protein, and the 18-kDa orfW product was 27% identical to the 16-kDa SpoIIAB protein. On the basis of this clear evolutionary conservation, we speculate these protein pairs regulate their respective sigma factors by a similar molecular mechanism and that the spoIIA and sigB operons might control divergent branches of stationary-phase gene expression.

Structural characterization of the Salmonella typhimurium LT2 umu operon

The umuDC operon of Escherichia coli encodes functions required for mutagenesis induced by radiation and a wide variety of chemicals. The closely related organism Salmonella typhimurium is markedly less mutable than E. coli, but a umu homolog has recently been identified and cloned from the LT2 subline. In this study the nucleotide sequence and structure of the S. typhimurium LT2 umu operon have been determined and its gene products have been identified so that the molecular basis of umu activity might be understood more fully. S. typhimurium LT2 umu consists of a smaller 417-base-pair (bp) umuD gene ending 2 bp upstream of a larger 1,266-bp umuC gene. The only apparent structural difference between the two operons is the lack of gene overlap. An SOS box identical to that found in E. coli is present in the promoter region upstream of umuD. The calculated molecular masses of the umuD and umuC gene products were 15.3 and 47.8 kilodaltons, respectively, which agree with figures determined by transpositional disruption and maxicell analysis. The S. typhimurium and E. coli umuD sequences were 68% homologous and encoded products with 71% amino acid identity; the umuC sequences were 71% homologous and encoded products with 83% amino acid identity. Furthermore, the potential UmuD cleavage site and associated catalytic sites could be identified. Thus the very different mutagenic responses of S. typhimurium LT2 and E. coli cannot be accounted for by gross differences in operon structure or gene products. Rather, the ability of the cloned S. typhimurium umuD gene to give stronger complementation of E. coli umuD77 mutants in the absence of a functional umuC gene suggests that Salmonella UmuC protein normally constrains UmuD protein activity.

Enhanced conditions for DNA fingerprinting with biotinylated M13 bacteriophage

Deoxyribonucleic acid (DNA) fingerprints are Southern blots which have a pattern resembling bar codes. The pattern is created by DNA probes that bind to variable-length repeated sequences of human genomic DNA digested with restriction endonucleases. To improve DNA fingerprints obtained with biotin-labeled M13mp8 replicative form (RF) bacteriophage as the gene probe, the conditions for hybridization and the subsequent washing steps of the filter were refined. Experiments were conducted varying the electrophoresis time, blotting membranes, hybridization solution, and posthybridization washes. The simplicity, sensitivity, and reliability of this nonistopic technique make possible its application for identification of individuals within a species, for parentage testing, and for monitoring bone marrow transplantation.

Recurrent inguinal hernia in relation to ideal body weight

The records of 686 patients who underwent herniorrhaphy for primary or initially recurrent inguinal hernia during the years 1975 through 1985 were reviewed. Patients were divided into groups according to percentage of ideal body weight. Analysis showed that, compared with the patients with primary hernia, a larger proportion of patients with recurrent hernia were near or below ideal body weight. A follow-up survey of 64 patients who underwent primary repair of hernia indicated that the percentage of ideal body weight of a patient had no apparent effect on the recurrence rate of inguinal hernia.

Tobacco, alcohol, and marijuana use among black adolescents: a comparison across gender, grade, and school environment

Self-report measures of tobacco, alcohol, and marijuana use were administered to 2,748 black adolescents, grades 7 through 12. The proportion of students who had tried any of the substances increased by grade. Males and females were not significantly different in their use of cigarettes and alcohol. Males were more likely to have tried smokeless tobacco, smoked marijuana, and used combinations of substances. Females who reported using more than one substance preferred the combination of cigarettes and alcohol. Significant effects of school environment were noted. Increasing age-related experimentation is exacerbated by school setting (junior high versus senior high). Given that blacks have disproportionately high cancer prevalence and mortality rates, intervention programs may also need to consider school environment, substance specific initiation points, and combined use preferences in order to maximize the desired effect within this population.

Isolation of a secY homologue from Bacillus subtilis: evidence for a common protein export pathway in eubacteria

Genetic and biochemical studies have shown that the product of the Escherichia coli secY gene is an integral membrane protein with a central role in protein secretion. We found the Bacillus subtilis secY homologue within the spc-alpha ribosomal protein operon at the same position occupied by E. coli secY. B. subtilis secY coded for a hypothetical product 41% identical to E. coli SecY, a protein thought to contain 10 membrane-spanning segments and 11 hydrophilic regions, six of which are exposed to the cytoplasm and five to the periplasm. We predicted similar segments in B. subtilis SecY, and the primary sequences of the second and third cytoplasmic regions and the first, second, fourth, fifth, seventh, and tenth membrane segments were particularly conserved, sharing greater than 50% identity with E. coli SecY. We propose that the conserved cytoplasmic regions interact with similar cytoplasmic secretion factors in both organisms and that the conserved membrane-spanning segments actively participate in protein export. Our results suggest that despite the evolutionary differences reflected in cell wall architecture, Gram-negative and Gram-positive bacteria possess a similar protein export apparatus.

Cloning of Salmonella typhimurium DNA encoding mutagenic DNA repair

Mutagenic DNA repair in Escherichia coli is encoded by the umuDC operon. Salmonella typhimurium DNA which has homology with E. coli umuC and is able to complement E. coli umuC122::Tn5 and umuC36 mutations has been cloned. Complementation of umuD44 mutants and hybridization with E. coli umuD also occurred, but these activities were much weaker than with umuC. Restriction enzyme mapping indicated that the composition of the cloned fragment is different from the E. coli umuDC operon. Therefore, a umu-like function of S. typhimurium has been found; the phenotype of this function is weaker than that of its E. coli counterpart, which is consistent with the weak mutagenic response of S. typhimurium to UV compared with the response in E. coli.

Mutagenic DNA repair genes on plasmids from the 'pre-antibiotic era'

Resistance transfer factors are natural conjugative plasmids encoding antibiotic resistance. Some also encode mutagenic DNA repair genes giving resistance to DNA damage and induced mutagenesis. It has been shown that antibiotic resistance has been acquired by recent transposition events; however, we show here that mutagenic repair genes existed much earlier on these types of plasmids. Conjugative plasmids from eight incompatibility groups from the Murray collection of 'pre-antibiotic era' enterobacteria were tested for complementation of mutagenic repair-deficient Escherichia coli umuC36. Although none of these plasmids carry transposon-encoded drug resistance genes, IncI1 and IncB plasmids were identified which restored ultraviolet resistance and induced mutability to umuC36 mutants. Furthermore they increased the UV resistance and induced mutability of wild-type E. coli, Klebsiella aerogenes and Citrobacter intermedius, thus showing that they could confer a general selective advantage to a variety of hosts. Like known mutagenic repair genes, complementation by these plasmid genes required the SOS response of the host cell. Nucleotide hybridisation showed that these plasmids harboured sequences similar to the impCAB locus, the mutagenic repair operon of modern-day IncI1 plasmids. The evolution of mutagenic repair genes is discussed.

Gene encoding the alpha core subunit of Bacillus subtilis RNA polymerase is cotranscribed with the genes for initiation factor 1 and ribosomal proteins B, S13, S11, and L17

We describe the genetic and transcriptional organization of the promoter-distal portion of the Bacillus subtilis alpha operon. By DNA sequence analysis of the region surrounding rpoA, the gene for the alpha core subunit of RNA polymerase, we identified six open reading frames by the similarity of their products to their counterparts in the Escherichia coli transcriptional and translational apparatus. Gene order in this region, given by gene product, was IF1-B-S13-S11-alpha-L17. Gene order in E. coli is similar but not identical: SecY-B-S13-S11-S4-alpha-L17. The B. subtilis alpha region differed most strikingly from E. coli in the presence of IF1 and the absence of ribosomal protein S4, which is the translational regulator of the E. coli alpha operon. In place of the gene for S4, B. subtilis had a 177-base-pair intercistronic region containing two possible promoter sequences. However, experiments with S1 mapping of in vivo transcripts, gene disruptions in the alpha region, and a single-copy transcriptional fusion vector all suggested that these possible promoters were largely inactive during logarithmic growth, that the major promoter for the alpha operon lay upstream from the region cloned, and that the genes in the IF1 to L17 interval were cotranscribed. Thus, the transcriptional organization of the region resembles that of E. coli, wherein the alpha operon is transcribed primarily from the upstream spc promoter, but the absence of the S4 gene suggests that the translational regulation of the region may differ more fundamentally.

Radical initiated alpha-tocopherol depletion and lipid peroxidation in mitochondrial membranes

The relationships between antioxidant status, lipid peroxidation and membrane protein integrity have been studied in an isolated mitochondrial membrane system. Tocopherol was shown to be present in both the outer and inner membrane of normal rat liver mitochondria; 77.3 and 22.3% of the total alpha-tocopherol was present in the outer and inner membranes, respectively. The endogenous alpha-tocopherol was depleted in a time-dependent manner by low levels of ferrous iron and by irradiation in the presence or absence of ferrous iron. This antioxidant depletion was followed by the appearance of lipid hydroperoxides. Fragmentation of monoamine oxidase, an integral outer membrane protein, was observed at irradiation doses that caused by antioxidant depletion and peroxide generation.

A continuous-flow automated assay for iodometric estimation of hydroperoxides

An iodometric method for the analysis of hydroperoxides has been automated to allow analysis of aqueous biological samples (containing less than 20 mg/ml protein) and lipid hydroperoxide extracts. The evolution of triiodide ions is measured spectrophotometrically at 360 nm. Dependent on the type of sample, 30-60 samples can be analyzed per hour and the system allows detection of less than 100 pmol of peroxide. The assay is linear over a range of 100 pmol to 25 nmol. The sample volume used routinely was 80 microliters.

Two mRNAs that differ by two nontemplated nucleotides encode the amino coterminal proteins P and V of the paramyxovirus SV5

The "P" gene of the paramyxovirus SV5 encodes two known proteins, P (Mr approximately equal to 44,000) and V (Mr approximately equal to 24,000). The complete nucleotide sequence of the "P" gene has been obtained and is found to contain two open reading frames, neither of which is large enough to encode the P protein. We have shown that the P and V proteins are translated from two mRNAs that differ by the presence of two nontemplated G residues in the P mRNA. These two additional nucleotides convert the two open reading frames to one of 392 amino acids. The P and V proteins are amino coterminal and have 164 amino acids in common. The unique C terminus of V consists of a cysteine-rich region that resembles a cysteine-rich metal binding domain. An open reading frame that contains this cysteine-rich region exists in all other paramyxovirus "P" gene sequences examined, which suggests that it may have important biological significance.

Frameshift mutagenesis by chloroquine in Escherichia coli and Salmonella typhimurium

Chloroquine can be detected as a direct-acting mutagen in plate-incorporation assays using the excision-deficient Salmonella typhimurium strain TA97, but very much more effectively using the repair-proficient Escherichia coli strain DG1669 which carries the lacZ19124 marker. When tested at concentrations of 200-1000 micrograms/plate with strain DG1669, the mutagenicity of chloroquine is enhanced by the addition of Aroclor-induced rat-liver S9. Further experiments indicated that chloroquine-induced reversion frequencies were essentially identical in wild-type, recA, umuC and uvrC derivatives of DG1669, as well as in strains carrying the mutation enhancing plasmid pKM101, over a wide range of doses (0-1200 micrograms/plate). These results suggest that neither excision repair nor SOS-type repair are important in chloroquine-induced frameshift mutagenesis.

RecA-independent mutagenesis in Escherichia coli may be subject to glucose repression

The frameshift mutagen 9-aminoacridine (9AA) causes DNA damage via a recA+-independent mechanism in Escherichia coli. In this study we have exposed E. coli cells carrying the lacZ19124 frameshift marker to 9AA in defined minimal media, washed them, and plated to score for Lac+ revertants. Our results show that 9AA-induced reversion to Lac+ occurs in the absence of any exogenous carbon source and when cells are plated on media which do not allow much, if any, cell replication prior to expression of the revertant phenotype. When glycerol (1% w/v) was added to the liquid treatment medium, the number of Lac+ E. coli revertants was similar to that obtained when no carbon source was present. By contrast the addition of glucose (1% w/v) during the mutagenesis treatment caused a significant decrease in the number of revertants. Further experiments indicate that the repressing effects of glucose may be due to a reduction in cAMP concentration, since 9AA mutagenesis was abolished in a cya strain in which no adenylate cyclase is produced. These results are consistent with (but do not prove) the notion that at least one part of the process leading to 9AA mutagenesis is subject to catabolite repression.

Gene encoding the 37,000-dalton minor sigma factor of Bacillus subtilis RNA polymerase: isolation, nucleotide sequence, chromosomal locus, and cryptic function

We began an analysis of rpoF, the gene encoding the cryptic, 37,000-dalton minor sigma factor (sigma-37) of Bacillus subtilis RNA polymerase. Using antibody raised against sigma-37 holoenzyme to probe a lambda gt11 expression vector library, we isolated a 901-base-pair EcoRI fragment that expressed the COOH-terminal half of sigma-37 fused to lacZ. We used this fragment as a hybridization probe to isolate the entire rpoF gene and additional flanking sequences. Identity of the cloned gene was confirmed by the size and immunological reaction of its product expressed in Escherichia coli and, after DNA sequencing, by the homology of its predicted product (264 residues; 30,143 daltons) with other sigma factors. The DNA sequence also suggested that rpoF may lie in a gene cluster. Upstream of rpoF was an open reading frame that would encode a protein of 17,992 daltons; this frame overlapped the rpoF-coding sequence by 41 base pairs. Immediately following rpoF was a reading frame that would encode a protein of at least 20,000 daltons; expression of this region may be translationally coupled to that of rpoF. By plasmid integration and PBS1 transduction, we found the chromosomal locus of rpoF linked to ddl and dal at 40 degrees on the B. subtilis map and near no known lesions affecting growth regulation or development. Further, an rpoF null mutation resulting from gene disruption had no effect on cell growth or sporulation in rich medium, suggesting that sigma-37 may partly control a regulon not directly involved in the sporulation process.

Free-radical-mediated fragmentation of monoamine oxidase in the mitochondrial membrane. Roles for lipid radicals

A flux of hydroxyl radicals generated by gamma-irradiation can fragment monoamine oxidase in the membrane of submitochondrial particles. This fragmentation can be inhibited by mannitol and in addition is more extensive in monoamine oxidase preparations that have been depleted of lipid. This latter observation is consistent with the higher yields of fragmentation induced by hydroxyl radicals in soluble proteins in the absence of added lipids. In the absence of oxygen, gamma-irradiation of submitochondrial particles leads to cross-linking reactions. A flux of hydroperoxyl radicals also causes fragmentation, whereas one of superoxide is virtually inactive in this respect. The irradiation of submitochondrial particles leads in addition to the accumulation of products of lipid peroxidation. When these irradiated preparations are exposed to ferrous or cupric salts a further fragmentation of monoamine oxidase ensues, especially at acid pH. These transition-metal-catalysed reactions do not occur with irradiated preparations depleted of lipid, and the post-irradiation protein modifications are concomitant with further lipid peroxidation. The data indicate roles for lipid radicals in both fragmentation and cross-linking reactions of proteins in biological membranes. These reactions may have an important bearing on control of protein activity and of protein turnover in membranes.

RecA-independent mutagenesis in Escherichia coli: effects of umuC and mucB mutations

We have studied the effects of a umuC mutation on reversion of the lacZ19124 and lacZ19136 frameshift markers of Escherichia coli. Introduction of a umuC::Tn5 mutation into a strain carrying the lacZ19136 marker resulted in enhanced reversion by 9-aminoacridine and the acridine half-mustard ICR191, whereas reversion of the lacZ19124 marker was decreased (but not abolished) in a umuC strain. The reversion frequency of the lacZ19136 marker was decreased by the presence of plasmid pKM101, and further decreased by a derivative of pKM101 in which the mucB gene was inactivated by a Tn5 insertion. The reversion frequency of the lacZ19124 marker was relatively unchanged by either plasmid. Since both 9-aminoacridine and ICR191 mutagenesis of these strains is independent of the recA+ and lexA+ gene products, these results may suggest a broader role for the UmuC protein in regulating induced mutation frequencies than has previously been suspected. The contrasting effects of the umuC and mucB mutations on reversion of the lacZ19136 marker may suggest a copy number effect, or perhaps more likely that there are inherent (functional) differences between the UmuC and MucB proteins.

Frameshift mutagenesis by 9-aminoacridine and ICR191 in Escherichia coli: effects of uvrB, recA and lexA mutations and of plasmid pKM101

We have studied the effects of different repair capacities on reversion of two Escherichia coli strains (lacZ19124 and lacZ19136) by 9-aminoacridine (9AA) and the acridine half-mustard ICR191. Introduction of a uvrB mutation into these strains led to enhanced ICR191-induced reversion of lacZ19136 and reduced ICR191-induced reversion of lacZ19124. 9AA-induced reversion of lacZ19124 was essentially unchanged while reversion of lacZ19136 was reduced. Plasmid pKM101 reduced reversion of the two markers by each of the mutagens, except in the case of ICR191-induced reversion of the lacZ19124 marker where mutagenesis was slightly enhanced. Mutations in the recA and lexA genes had minimal effects on ICR191- and on 9AA-induced reversion of the lacZ markers; although 9AA-induced reversion of the lacZ19124 marker was somewhat reduced, most of the other results indicated that mutation yields were if anything higher in the recA or lexA backgrounds. Mutagenesis by 9AA and ICR191 would therefore appear to occur independently of the inducible error-prone repair process commonly referred to as SOS repair.

Metronidazole prevention of serum liver enzyme abnormalities during total parenteral nutrition

Abnormal serum liver enzymes are common in adults receiving total parenteral nutrition (TPN). The mechanism(s) responsible for these changes is unclear. One hypothesis is that there is overgrowth of intestinal anaerobic bacteria with subsequent toxic effects on the liver from endotoxins and/or bile acids. A retrospective survey of patients receiving TPN was undertaken. The patients were divided into two matched groups. One group had received metronidazole, a drug that suppresses anaerobic bacteria, while the other group had not. The administration of metronidazole during TPN was associated with prevention of the expected rise of serum alkaline phosphatase, gamma glutamyl transpeptidase, and aspartate amino-transferase. This study supports the concept that anerobic intestinal bacteria may be involved in the pathogenesis of liver changes commonly observed during TPN.

Anaplastic myeloma in systemic lupus erythematosus

We describe a patient with systemic lupus erythematosus who developed an unusual form of anaplastic myeloma. Possible relationships between the two disease, and the role played by immunosuppressive therapy, are discussed.

Olfactory neuroblastoma. A case report in an African child

The case is described of an eight-year-old Nigerian boy who died from olfactory neuroblastoma which presented with nasal obstruction and epistaxis. Autopsy showed intracranial extension of the tumour into the frontal lobe, and histology revealed undifferentiated neuroblasts, forming rosettes in some areas and producing tangled neurofibrils in others. The histogenesis of the tumour and its diagnosis are briefly discussed.

Protein AA amyloidosis in Nigeria

Eight cases of multi-system amyloid have been found in 4235 autopsies (0.2%) performed at University College Hospital, Ibadan, Nigeria between 1970 and 1979. Blocks and sections of seven cases showed the organ distribution associated with secondary amyloid, involving kidney, spleen and liver. Potassium permanganate oxidation prior to Congo Red staining showed that all seven cases contained protein AA amyloid. Five patients had tuberculosis but in two patients there was no recognized cause, idiopathic AA amyloid. Patients usually presented with nephrotic syndrome or renal failure and hypertension was absent. There appears to be a low incidence of amyloidosis in Africans, despite the occurrence of a large number of potential amyloidogenic stimuli, indicating the importance of individual host reactivity and failure of amyloid degradation in the causation of amyloidosis.

A double-blind clinical trial of isoniazid in Huntington disease

Isoniazid (INH) was given to nine patients with Huntington disease (HD) in a double-blind, placebo-controlled crossover trial. In an earlier open trial, three of six patients had improved, and one of them remained improved after 7 years on INH. Only one patient benefited in the present trial. All patients excreted small amounts of hydrazine in their urine while taking INH, and it is this INH metabolic that elevates GABA content in brain. GABA concentrations were markedly increased in CSF during INH therapy. Lack of clinical improvement in most HD patients despite elevation of brain GABA content suggests that in the minority who are benefited, INH may be acting by some mechanism other than increase of GABAergic neuronal function.

C4 photosynthesis in Spartina townsendii at low and high temperatures

The metabolism of (14)CO2 in the cool temperate saltmarsh grass Spartina townsendii was investigated in plants grown in their natural habitats at two temperatures. Both in the spring at 10°C and in the late summer at 25°C radioactivity was initially incorporated into the organic acids malate and aspartate and then transferred to 3-phosphoglycerate in the manner characteristic of the C4 pathway of photosynthesis. Metabolism was not disrupted at the lower temperature as in some C4 plants. Radioactivity was transferred more slowly from malate into alanine, glycine and serine at 10°C, but sugars were labelled equally at both temperatures.

Location of gluconeogenesis from phosphoenolpyruvate in cotyledons of Cucurbita pepo

1. The aim of this work was to discover the location of the enzymes that convert phosphoenolpyruvate to fructose 6-phosphate during gluconeogenesis in fatty seeds. Cotyledons of 5-day-old dark-grown seedlings of marrow (Cucurbita pepo) were used as experimental material. 2. Cotyledons were separated into palisade and mesophyll tissue. Extracts of the two tissues had comparable activities of gluconeogenic enzymes. 3. Extracts of cotyledons were fractionated by density gradient centrifugation to yeild mitochondria and glyoxysomes, and by gel filtration to yield proplastids. The isolated organelles retained their characteristic ultrastructure and appreciable amounts of marker enzymes. The proportions of the total activities of phosphoglyceromutase and fructose-1, 6-diphosphatase recovered in the mitochondrial and glyoxysomal preparations were insignificant. The same was true for the activities of phosphoglyceromutase and phosphopyruvate hydratase found in the proplastid preparations. 4. Extracts of a number of other gluconeigenic plant tissues were centrifuged at 2500 times g to yield particulate preparations. None of these preparations contained a significant proportion of the total activity of phosphoglyceromutase. 5. It is suggested that gluconeogenesis from phosphoenolpyruvate in plants occurs in the cytoplasm.