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S Aymerich

Publications and source records attributed to S Aymerich.

23 records · Page 2Linked to original sources
PubMed1986

5'-noncoding region sacR is the target of all identified regulation affecting the levansucrase gene in Bacillus subtilis.

The regulation of the levansucrase gene sacB was studied in Bacillus subtilis strains. Fusions were constructed in which genes of cytoplasmic proteins such as lacZ were placed immediately downstream from sacR, the regulatory region located upstream from sacB. These fusions were introduced in mutants affected in sacB regulation. In all cases the marker gene was affected in the same way as sacB by the genetic context. This result is of particular interest for the sacU pleiotropic mutations, which affect sacB expression and other cellular functions such as the synthesis of several exocellular enzymes. We also showed that strains harboring sacU+ or sacU-hyperproducing alleles contained different amounts of sacB mRNA, which was proportional to their levansucrase secretion. We concluded that the sacU gene does not affect sacB expression at the level of secretion but acts on a target within sacR. We discuss the possibility that sacU acts on a part of sacR, a homologous copy of which was found upstream from the gene of another sacU-dependent secreted enzyme of B. subtilis, beta-glucanase.

Bacillus subtilis↗
PubMed1985

The DNA sequence of the gene for the secreted Bacillus subtilis enzyme levansucrase and its genetic control sites.

We present the sequence of a 2 kb fragment of the Bacillus subtilis Marburg genome containing sacB, the structural gene of levansucrase, a secreted enzyme inducible by sucrose. The peptide sequence deduced for the secreted enzyme is very similar to that directly determined by Delfour (1981) for levansucrase of the non-Marburg strain BS5. The peptide sequence is preceded by a 29 amino acid signal peptide. Codon usage in sacB is rather different from that in the sequenced genes of other secreted enzymes in B. subtilis, especially alpha-amylase. Genetic evidence has shown that the sacB promotor is rather far from the beginning of sacB (200 bp or more). The 200 bp region preceding sacB shows some of the features of an attenuator. A preliminary discussion of the putative workings and roles of this attenuator-like structure is proposed. sacRc mutations, which allow constitutive expression of levansucrase, have been located within the 450 bp upstream of sacB. It is shown that sacRc and sacR+ alleles control in cis the expression of the adjacent sacB gene.

Amino Acid Sequence↗
PubMedDate not supplied

[Genetic analysis of sacR, a cis-regulator of levan-saccharase synthesis of Bacillus subtilis].

The phenotypical and physical characterization of point mutations and deletions affecting sacR were analysed. The 2 X 28-bp palindromic region present within sacR was responsible for sacB inducibility by sucrose. The sacR mutations also affected sacB expression in Escherichia coli, suggesting that the palindromic region is a transcriptional terminator. It is difficult to apply classical bacterial models of negative or positive regulation to sacR function in B. subtilis. We propose that sacR works as a transcriptional attenuator. Our hypothesis is similar to that proposed for the regulation of the tryptophan operon in B. subtilis: the attenuation of sacB transcription could be modulated by a diffusible regulator whose activity is controlled by the inducer, sucrose. Furthermore, we have observed very strong sequence homologies between sacR and the region located upstream from the gene of another secreted enzyme from B. subtilis, beta-glucanase. We propose a preliminary discussion of this observation.

Bacillus subtilis↗