F sex factor of Escherichia coli K-12 codes for a single-stranded DNA binding protein.

Abstract

In E. coli K-12 strains that carry the mutation ssb-1 in the gene for single-stranded DNA binding protein, the presence of the F sex factor partially reverses the temperature-sensitive growth phenotype caused by the mutation. The region of F (EcoRI fragment 3) responsible for this compensation was identified and subcloned onto pBR322. A BamHI cleavage site intersects the essential coding region for this F function. By using this site, mutational blocks in the function were constructed and used to identify a protein product (MW .apprx. 22,000, slightly larger than the E. coli K-12 single-stranded DNA binding protein) which is correlated with the ssb-1-complementing activity. Labeled extracts from maxicells were used to show that this protein binds tightly to single-stranded DNA. The gene on F that codes for this protein is denoted ssf and is located at .apprx. 55.2 kilobases on the standard map of F, in the region transferred very early during conjugation.