THE SBCCD PROTEIN OF ESCHERICHIA-COLI IS RELATED TO 2 PUTATIVE NUCLEASES IN THE UVRA SUPERFAMILY OF NUCLEOTIDE-BINDING PROTEINS

The derived amino-acid sequences of the proteins encoded by E. coli genes sbcC and sbcD have been compared with other protein sequences using computer assisted methods. This work has shown that SbcC and D, which inhibit the propagation of replicons containing long palindromic DNA sequences, are distantly related to two putative bacteriophage nucleases. These nucleases both comprise two polypeptide chains which are the products of genes 46 and 47 of bacteriophage T4 (gp 46 and gp 47) and genes D13 and D12 of bacteriophage T5 (gp D13 and gp D12). The comparisons reveal that SbcC, gp 46 and gp D13 are more closely related to each other than are SbcD, gp 47 and gp D12. SbcC appears to have undergone a partial duplication of an ancestral sequence. These proteins all contain motifs common to the superfamily of nucleotide-binding proteins that includes UvrA and the cystic fibrosis transmembrane regulator CFTR.