Identification of psiB genes of plasmids F and R6-5. Molecular basis for psiB enhanced expression in plasmid R6-5.
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.
Dutreix
M
M
GEMC, Enzymologie, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
Bäckman
A
A
Célérier
J
J
Bagdasarian
M M
MM
Sommer
S
S
Bailone
A
A
Devoret
R
R
Bagdasarian
M
M
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D005144:F Factor; D005796:Genes; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D011815:R Factors; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification; D011994:Recombinant Proteins / Q000302:isolation & purification; D015183:Restriction Mapping
D001426:Bacterial Proteins; C058074:PsiB protein, Bacteria; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins