CLONING AND SEQUENCING THE BACILLUS-SUBTI LIS CHROMOSOME FRAGMENT COMPLEMENTARY TO THE EXOA MUTATION OF BACILLUS-SUBTILIS AND SBCB OF ESCHERICHIA-COLI

A 3279-bp fragment of the Bacillus subtilis chromosome was cloned. Thi s 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 se quence of the Bac. subtilis gene encoding the structure of exonuclease I was determined. The amino-acid sequence of this enzyme proved to ha ve 29.7% homology with the amino-acid sequence of E. coli exonuclease I.