GENETIC-RECOMBINATION IN BACILLUS-SUBTILIS 168 - EFFECT OF RECN, RECF, RECH AND ADDAB MUTATIONS ON DNA-REPAIR AND RECOMBINATION

A recN- (recN1) strain of Bacillus subtilis was constructed. The effec ts of this and recF, recH and addAB mutations on recombination profici ency were tested. Mutations in the recN, recF, recH and addAB genes, w hen present in an otherwise Rec+ B. subtilis strain, did not affect ge netic exchange. Strains carrying different combinations of mutations i n these genes were constructed and examined for their sensitivity to 4 -nitroquinoline-1-oxide (4NQO) and recombination proficiency. The recH mutation did not affect the 4NQO sensitivity of recN and recF cells a nd it only marginally affected that of addA addB cells. However, it re duced genetic recombination in these cells 10(2)- to 10(4)-fold. The a ddA addB mutations increased the 4NQO sensitivity of recF and recN cel ls, but completely blocked genetic recombination of recF cells and mar ginally affected recombination in recN cells. The recN mutation did no t affect the recombinational capacity of recF cells. These data indica te that the recN gene product is required for DNA repair and recombina tion and that the recF, recH and addAB genes provide overlapping activ ities that compensate for the effects of single mutants proficiency. W e proposed that the recF, recH, recB and addA gene products define fou r different epistatic groups.