期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2012
卷号：109
期号：34
页码：13596-13601
DOI：10.1073/pnas.1210040109
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Physical biochemical techniques are used to establish the structure, subunit stoichiometry, and assembly pathway of the primosome complex of the bacteriophage T4 DNA replication system. Analytical ultracentrifugation and fluorescence anisotropy methods show that the functional T4 primosome consists of six gp41 helicase subunits that assemble into a hexagon, driven by the binding of six NTPs (or six nonhydrolyzable GTP{gamma}S analogues) that are located at and stabilize the intersubunit interfaces, together with a single tightly bound gp61 primase subunit. Assembling the components of the primosome onto a model DNA replication fork is a multistep process, but equilibrium cannot be reached along all mixing pathways. Producing a functional complex requires that the helicase hexamer be assembled in the presence of the DNA replication fork construct prior to the addition of the primase to avoid the formation of metastable DNA-protein aggregates. The gp41 helicase hexamer binds weakly to fork DNA in the absence of primase, but forms a much more stable primosome complex that expresses full and functional helicase (and primase) activities when bound to a gp61 primase subunit at a helicase:primase subunit ratio of 6:1. The presence of additional primase subunits does not change the molecular mass or helicase activity of the primosome, but significantly inhibits its primase activity. We develop both an assembly pathway and a minimal mechanistic model for the structure and function of the T4 primosome that are likely to be relevant to the assembly and function of the replication primosome subassemblies of higher organisms as well.
