Loss-of-function mutations in yjbD result in ClpX- and CipP-independent competence development of Bacillus subtilis

Nakano, MM Hajarizadeh, F Zhu, Y Zuber, P

Mm. Nakano et al., Loss-of-function mutations in yjbD result in ClpX- and CipP-independent competence development of Bacillus subtilis, MOL MICROB, 42(2), 2001, pp. 383-394

71

INGLESE

Article

Microbiology

MOLECULAR MICROBIOLOGY

0950-382X → ACNP

42

2

2001

383 - 394

ISI

0950-382X(200110)42:2<383:LMIYRI>2.0.ZU;2-7

Mutations in clpP and clpX have pleiotropic effects on growth and developme ntally regulated gene expression in Bacillus subtilis. ClpP and ClpX are ne eded for expression of comK, encoding the competence transcription factor r equired for the expression of genes within the competence regulon. ClpP, in combination with the ATPase ClpC, degrades the inhibitor of ComK, MecA. Pr oteolysis of MecA is stimulated by a small protein, ComS, which interacts w ith MecA. Suppressor mutations (cxs) were isolated that bypass the requirem ent for clpX for comK expression. These were found also to overcome the def ect in comK expression conferred by a clpP mutation. These mutations were i dentified as missense mutations (cxs-5, -7 and -12) and a nonsense (UAG) co don substitution (cxs-10) in the yjbD coding sequence in a locus linked to mecA. That a yjbD disruption confers the cxs phenotype, together with its c omplementation by an ectopically expressed copy of yjbD, indicated that the suppressor alleles bear recessive, loss-of-function mutations of yjbD. Clp P- and ClpX-independent comK expression rendered by inactivation of yjbD wa s still medium-dependent and required ComS. MecA levels in a clpP-yjbD muta nt were lower that those of clpP mutant cells and ComK protein concentratio n in the clpP mutant was restored to wild-type levels by the yjbD mutation. Consequently, the yjbD mutation bypasses the defect in competence developm ent conferred by clpP and clpX. YjbD protein is barely detectable in wildty pe cells, but is present in large amounts in the clpP mutant cells. The res ults suggest that the role of ClpP in competence development is to degrade YjbD protein so that ComS can productively interact with the MecA-ClpC-ComK complex. Alternatively, the result could suggest that YjbD has a negative effect on regulated proteolysis and that MecA is degraded independently of ClpP when YjbD is absent.