Suppression of early competence mutations in Bacillus subtilis by mec mutations.

Although competence normally develops only in glucose-minimal salts media, mecA and mecB mutations permit the expression of competence and of late competence genes in complex media as well (D. Dubnau and M. Roggiani, J. Bacteriol. 172:4048-4055, 1990). The expression of late competence genes is dependent on the products of the regulatory genes comA, comB, comP, sin, abrB, spo0H, and spo0A. We show here that this list must be extended to include degU, csh-293, and spo0K. mecA and -B mutations bypass most of these requirements, making the expression of late competence genes and of competence itself independent of all of these regulatory genes, with the exceptions of spo0A and spo0K (in the case of mecB). The expression of late competence genes in mec mutants that are deficient for each of the bypassed regulatory functions is still under growth stage-specific regulation. The implications of these findings are discussed, and a provisional scheme for the flow of information during the development of competence is proposed.     

Growth medium-independent genetic competence mutants of Bacillus subtilis.

The development of competence in Bacillus subtilis is normally dependent on the growth medium. Expression of late competence genes occurs in glucose-minimal salts-based media but not in complex media. Expression is also inhibited when glutamine is added to competence medium and when glycerol is substituted for glucose. Mutations have been identified in two regulatory loci, mecA and mecB, which render competence development independent of these variables. Although in mec mutants the expression of late competence genes, as well as of competence itself, occurred in all media tested, this expression was still growth stage regulated. Thus at least some forms of medium-dependent and growth stage-specific regulation are genetically separable. One of the mecB mutations (mecB31) conferred oligosporogenicity. The mecB mutations were tightly linked by transformation to rif, lpm, and std markers and were located between rif-2103 and cysA14. The mecA42 mutant was linked by transduction to argC4.     

Fungal catabolic gene regulation: Molecular genetic analysis of theamdS gene ofAspergillus nidulans

Aspergillus nidulans is an excellent experimental organism for the study of gene regulation. Genetic and molecular analyses oftrans-acting andcis-acting mutations have revealed a complex pattern of regulation involving multiple independent controls. Expression of theamdS gene is regulated by thefacB andamdA genes which encode positively acting regulatory proteins mediating a major and a minor form of acetate induction respectively. The product of theamdR gene mediates omega amino acid induction ofamdS. The binding sites for each of these proteins have been localised throughamdS cis-acting mutations which specifically affect the interaction with the regulatory protein. The global controls of nitrogen metabolite repression and carbon catabolite repression regulate the expression of many catabolic genes, includingamdS. Nitrogen control is exerted through the positively actingareA gene product and carbon control is dependent on thecreA gene product. Each of the characterized regulatory genes encodes a DNA-binding protein which recognises particular sequences in theamdS promoter to activate or repress gene expression. In addition, there is evidence for other genetically uncharacterised proteins, including a CCAAT-binding complex, which interact with the 5 region of theamdS gene.     

“The Image” of the Regulatory Gene in Experiments with Drosophila

The mutants referred to as facultative dominant lethals were selected in the progeny of gamma-irradiated Drosophila males. The mutant males were viable and fertile, though their crosses with females of the yellow line yielded no daughters. The mutations obtained differed from the common mutations by (1) extremely varying penetrance of F₁ hybrids from crosses with various lines; (2) the uncertain relationships between the mutant and normal alleles; (3) the different expression in somatic and germ cells; (4) the dependence of the expression on the sex of the parent that was the donor of the mutation; (5) the mass morphosis formation and (6) the frequent reversal to the norm. These mutations are assigned to the regulatory group and their specific expression (see above) can be helpful in identifying regulatory gene mutations. We assume that the specific expression of the mutations studied is related to specific properties of the regulatory genes. These properties are as follows: (1) only one out of two homologous regulatory genes is in an active state, (2) in the haploid chromosome set, the regulatory gene is represented by several alleles (cys-alleles); (3) only one allele ensures the regulatory gene activity.     

Genetic Organization of the mecA Region in Methicillin-Susceptible and Methicillin-Resistant Strains of Staphylococcus sciuri

A homolog of the Staphylococcus aureus methicillin resistance gene mecA was recently shown to be ubiquitous in independent isolates of the animal species Staphylococcus sciuri. The mecA gene homolog and regions flanking it were cloned and sequenced from four strains of S. sciuri: strain K1 (ATCC 29062), a representative of S. sciuri subsp. sciuri; two strains (K3 and K8) representing S. sciuri subsp. rodentius; and strain K11, a representative of S. sciuri subsp. carnaticum. Strains K1 and K11 were susceptible to methicillin, while strains K3 and K8 showed heterogeneous resistance. The mecA genes of strains K1 and K11 and one of the two copies of mecA (mecA1) present in strain K3 had virtually identical DNA sequences in the mecA gene and were similar in genetic organization in the flanking regions. In contrast, the single copy of mecA in strain K8 and the second copy of mecA (mecA2) in strain K3 had mecA DNA sequences identical to that of S. aureus mecA, and the mecA region in these two strains was also similar to that of the same region in the S. aureus strain used for comparison. Interestingly, an open reading frame defining an N-terminal truncated polypeptide, NTORF101, with a high degree of homology to a DNA segment in the hypervariable region of methicillin-resistant S. aureus (and also similar to the Escherichia coli gene ugpQ) was also identified downstream of the mecA homolog of strain K11, representing S. sciuri subsp. carnaticum. The ugpQ-like gene is not present in methicillin-susceptible strains of S. aureus. The presence of such a ugpQ-like gene together with the homolog of mecA in strain K11 supports the speculation that these genetic elements may be evolutionary relatives and/or precursors of the genetic determinant of methicillin resistance in S. aureus.     

Temporal and spatial control of expression of anthocyanin biosynthetic genes in developing flowers of Antirrhinum majus

The co-ordination of expression of anthocyanin biosynthetic genes was studied in developing flowers. Four genes encoding enzymes operating late in the anthocyanin biosynthetic pathway are induced together during flower development but the early steps appear to be induced more rapidly. Co-ordination of expression could imply a common regulatory mechanism controlling the expression of metabolically related genes. The data presented here show that while four genes may share such a mechanism for the control of their expression during flower development, different control processes regulate the early steps of the pathway. Spatially, gene expression is patterned across the flower and appears to be very similar for all the biosynthetic genes. However, the observed influence of the regulatory gene Delila shows that the spatial co-ordination of gene expression must involve more than one regulatory system. Delila itself appears to have a dual function, being required for activation of expression of the later genes in the flower tube but repressing chalcone synthase gene expression in the mesophyll of the corolla lobes. It is postulated that common signals induce the expression of genes in the pathway during flower development. The data presented here suggest that the same regulatory mechanism interprets these signals for four of the genes encoding the later biosynthetic enzymes, but that different or modified mechanisms interpret the signals to control expression of chalcone synthase and chalcone isomerase genes in Antirrhinum flowers.     

The products of glnL and glnG are bifunctional regulatory proteins

Summary The role of the two glnA linked genes, glnL and glnG, in regulation of glnA expression and nitrogen metabolism in Escherichia coli has been studied by analysis of 131 glnL and 164 glnG genetically characterized mutations. A comparison of phenotypes with genetic position was performed for all mutations in glnL and glnG. We determined the ability of mutants to derepress GS, to grow on a variety of nitrogen sources in the absence of glutamine, and to suppress the glutamine requirement caused by a glnF mutation. The results indicate that both glnL and glnG products mediate negative regulation of glnA. The glnG product, but not that of glnL, is required for derepression of glnA. Both glnL and glnG products are required for positive regulation of gene products involved in the utilization of poor nitrogen sources. In each gene, point mutations were found which confer a phenotype dramatically different than that caused by insertion mutations. These point mutations fall into several frequently occurring classes. The phenotypes of these classes suggests that each gene product has bifunctional regulatory properties. Further, each class tends to be located in only a portion of a gene suggesting that the region encoding each function is genetically distinct.The role of glutamine synthetase in the regulation of glnA expression was investigated using two-dimensional polyacrylamide gel electrophoresis on extracts of 38 GlnA^- mutants. Results of this analysis argue that glutamine synthetase is not structurally involved in the regulation of glnA expression.