Studies on in vitro DNA synthesis. Purification of the dna G gene product from Escherichia coli.

varphiX174 DNA-dependent dNMP incorporation is temperature-sensitive (ts) in extracts of uninfected E. coli dna A, B, C, D, E, and G ts strains. DNA synthesis can be restored in heat-inactivated extracts of various dna ts mutants by addition of extracts of wild-type or other dna ts mutants. A protein that restores activity to heat-inactivated extracts of dna G ts cells has been extensively purified. This protein has also been purified from dna G ts cells and is thermolabile when compared to the wild-type protein. The purified dna G protein has a molecular weight of about 60,000, is insensitive to N-ethylmaleimide, and binds poorly to DNA. It does not stimulate heat-inactivated crude extracts of dna B, C, D, or E ts cells and lacks detectable RNA and DNA polymerase activities.