Biological activity and a partial amino-acid sequence of Escherichia coli DNA-binding protein I isolated from overproducing cells.

Abstract

DNA-binding protein I from Escherichia coli was purified from cells carrying the ssb gene on a multicopy plasmid. In comparison to the strain without the recombinant plasmid the DNA-binding protein was over-produced more than 20-fold. The amount of the protein was measured after the purification steps by gel electrophoresis and radial immunodiffusion. The protein was purified to homogeneity and was active in replication assays like the wild-type DNA-binding protein. The assays were enzymatic replication of single-stranded and double-stranded fd DNA. E. coli DNA-binding protein I was further subjected to amino acid sequence analysis. A monomer of the protein consists of 187 residues which correspond to a molecular weight of 19715 with 5% error in analysis. The sequence of the amino-terminal 40 residues was determined and includes several basic residues of the protein. Sequence comparison between the DNA-binding protein I from E. coli and that coded by bacteriophage fd reveals similarities suggesting that DNA-binding protein I may use amino-terminal residues for binding to DNA like the phage protein.