Assembly of a chromosomal replication machine: two DNA polymerases, a clamp loader, and sliding clamps in one holoenzyme particle. III. Interface between two polymerases and the clamp loader.
The nine-subunit DNA polymerase (Pol) III* coupled to its beta sliding clamp is a rapid and highly processive replicating machine. The multiple subunits are needed for the complicated task of duplicating the Escherichia coli chromosome. In this report, Pol III* was constituted from individual pure proteins, and its structure was studied. Constitution of the Pol III* particle requires an ordered addition of the subunits, and the final structure contains 14 polypeptides in the ratio alpha 2 epsilon 2 theta 2 tau 2 gamma 2 delta 1 delta' 1 chi 1 psi 1. The structure can be summarized as being composed of two core polymerases (alpha epsilon theta) held together by a dimer of tau and one gamma complex clamp loader (gamma 2 delta 1 delta' 1 chi 1 psi 1) for loading beta onto DNA. At the center of the structure, the related tau and gamma subunits form a heterotetramer upon which the two core polymerases and clamp loader proteins assemble. The single copy nature of the delta, delta', chi, and psi subunits confers a structural asymmetry with respect to the two polymerases, presumably for the different functions of replicating the leading and lagging strands.
Onrust
R
R
Microbiology Department, Cornell University Medical College, New York, New York 10021, USA.
Finkelstein
J
J
Turner
J
J
Naktinis
V
V
O'Donnell
M
M
D002876:Chromosomes, Bacterial; D004258:DNA Polymerase III / Q000737:chemistry / Q000378:metabolism*; D004261:DNA Replication; D004259:DNA-Directed DNA Polymerase / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation
D007527:Isoenzymes; C023140:DNA replicase; D004258:DNA Polymerase III; D004259:DNA-Directed DNA Polymerase