THE MFD PROTEIN OF BACILLUS-SUBTILIS-168 IS INVOLVED IN BOTH TRANSCRIPTION-COUPLED DNA-REPAIR AND DNA RECOMBINATION

Inactivation of Bacillus subtilis orf1177 in an otherwise Rec(+) strai n reduced genetic exchange and DNA repair. When the mutation was trans ferred into a set of recombination-deficient and repair-deficient stra ins, the DNA repair and recombination ability of the double or triple mutant strains was drastically reduced. B. subtilis Orf1177 protein sh ares substantial homology with the Escherichia coli Mfd, RecG and UvrB proteins. In vivo analysis of UV-induced mutations suggests that Orf1 177 is necessary for strand-specific DNA repair, as is the case for th e E. coli Mfd protein. Therefore, orf1177 and Orf1177 were termed mfd gene and Mfd protein, respectively: The purified Mfd protein has a nat ive molecular mass of 140 kDa (expected molecular mass 133 kDa). The M fd protein is a sequence-independent DNA binding protein with weak ATP ase activity. The Mfd protein was able to displace in vitro B. subtili s or E. coli RNA polymerase stalled at a lesion. Therefore, Mfd protei n appears to target the transcribed strand for repair by recognizing a stalled RNA polymerase and dissociating it from the DNA. In addition, the strong recombination-deficient phenotype of mfd(-) rec(-) strains suggests that Mfd protein is involved in homologous DNA recombination . (C) 1996 Academic Press Limited