ROLE OF THE CORE DNA-POLYMERASE-III SUBUNITS AT THE REPLICATION FORK - ALPHA IS THE ONLY SUBUNIT REQUIRED FOR PROCESSIVE REPLICATION

The DNA polymerase III holoenzyme is composed of 10 subunits. The core of the polymerase contains the catalytic polymerase subunit, alpha, t he proofreading 3' --> 5' exonuclease, epsilon, and a subunit of unkno wn function, theta. The availability of the holoenzyme subunits in pur ified form has allowed us to investigate their roles at the replicatio n fork. We show here that of the three subunits in the core polymerase , only alpha is required to form processive replication forks that mov e at high rates and that exhibit coupled leading-and lagging-strand sy nthesis in vitro. Taken together with previous data this suggests that the primary determinant of replication fork processivity is the inter action between another holoenzyme subunit, tau, and the replication fo rk helicase, DnaB.