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

• Published in: The Journal of biological chemistry 1995-06, Vol.270 (22), p.13366-13377
• Main Authors: Onrust, R, Finkelstein, J, Turner, J, Naktinis, V, O'Donnell, M
• Format: Article
• Language: English
• Subjects: Chromosomes, Bacterial; DNA Polymerase III - chemistry; DNA Polymerase III - metabolism; DNA Replication; DNA-Directed DNA Polymerase - chemistry; DNA-Directed DNA Polymerase - metabolism; Escherichia coli; Escherichia coli - genetics; Isoenzymes - chemistry; Isoenzymes - metabolism; Protein Binding; Protein Conformation
• ISSN: 0021-9258
• DOI: 10.1074/jbc.270.22.13366

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.