Identification of psiB genes of plasmids F and R6-5. Molecular basis for psiB enhanced expression in plasmid R6-5

• Published in: Nucleic acids research 1988-11, Vol.16 (22), p.10669-10679
• Main Authors: DUTREIX, M, BÄCKMAN, A, CELERIER, J, BAGDASARIAN, M. M, SOMMER, S, BAILONE, A, DEVORET, R, BAGDASARIAN, M
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Bacterial Proteins - genetics; Base Sequence; Biological and medical sciences; Escherichia coli; F Factor; Fundamental and applied biological sciences. Psychology; Genes; Genes, Bacterial; Genes. Genome; Molecular and cellular biology; Molecular genetics; Molecular Sequence Data; R Factors; Recombinant Fusion Proteins - isolation & purification; Recombinant Proteins - isolation & purification; Restriction Mapping
• ISSN: 0305-1048; 1362-4962
• DOI: 10.1093/nar/16.22.10669

PsiB protein of plasmid R6-5 inhibits the induction of the SOS pathway. The F sex factor also carries a psiB gene homologous to that of R6-5. Yet, it fails to inhibit SOS induction. In order to solve this difference, we characterized the psiB genes of R6-5 and F. We found that (i) the sequences of the two psiB genes share extensive homology the predicted amino acid sequences of the two proteins differing by 5 residues, (ii) the expression of R6-5 psiB is 4 times higher than F psiB gene, (iii) in plasmid R6-5, a Tn10 transposon upstream from the psiB gene enhances psiB expression. Hence, the F sex factor may be unable to prevent SOS induction for two non-exclusive reasons: (i) F PsiB protein, being slightly different from R6-5, may be less active, (ii) the level of synthesis of F PsiB protein may be insufficient to prevent SOS induction.