[Cloning and sequencing of the chromosome fragment of Bacillus subtilis, complementary to the exoA mutation of Bacillus subtilis and sbcB of Escherichia coli].

A 3279-bp fragment of the Bacillus subtilis chromosome was cloned. This fragment completely restored exonuclease I activity in cells of the Escherichia coli Jm105 strain, which contained the sbcB mutation, and suppressed repair damage in cells of this mutant. The cloned fragment fully complemented a mutation that decreased exonuclease I activity in Bac. subtilis KU647 and KU1020 strains leading to the restoration of enzymatic activity and mutant phenotype suppression. The nucleotide sequence of the Bac. subtilis gene encoding the structure of exonuclease I was determined. The amino-acid sequence of this enzyme proved to have 29.7% homology with the amino-acid sequence of E. coli exonuclease I.