The DNA replication machine of a gram-positive organism

This report outlines the protein requirements and subunit organization of the DNA replication apparatus of Streptococcus pyogenes, a Gram-positive organism. Five proteins coordinate their actions to achieve rapid and processive DNA synthesis. These proteins are: the PolC DNA polymerase, tau, delta, delta', and beta. S. pyogenes dnaX encodes only the full-length tau, unlike the Escherichia coli system in which dnaX encodes two proteins, tau and gamma. The S. pyogenes tau binds PolC, but the interaction is not as firm as the corresponding interaction in E. coli, underlying the inability to purify a PolC holoenzyme from Gram-positive cells. The tau also binds the delta and delta' subunits to form a taudeltadelta' "clamp loader." PolC can assemble with taudeltadelta' to form a PolC.taudeltadelta' complex. After PolC.taudeltadelta' clamps beta to a primed site, it extends DNA 700 nucleotides/second in a highly processive fashion. Gram-positive cells contain a second DNA polymerase, encoded by dnaE, that has homology to the E. coli alpha subunit of E. coli DNA polymerase III. We show here that the S. pyogenes DnaE polymerase also functions with the beta clamp.