Conservation of structure and function of DNA replication protein A in the trypanosomatid Crithidia fasciculata.

Human replication protein A (RP-A) is a three-subunit protein that is required for simian virus 40 (SV40) replication in vitro. The trypanosome homologue of RP-A has been purified from Crithidia fasciculata. It is a 1:1:1 complex of three polypeptides of 51, 28, and 14 kDa, binds single-stranded DNA via the large subunit, and is localized within the nucleus. C. fasciculata RP-A substitutes for human RP-A in the large tumor antigen-dependent unwinding of the SV40 origin of replication and stimulates both DNA synthesis and DNA priming by human DNA polymerase alpha/primase, but it does not support efficient SV40 DNA replication in vitro. This extraordinary conservation of structure and function between human and trypanosome RP-A suggests that the mechanism of DNA replication, at both the initiation and the elongation level, is conserved in organisms that diverged from the main eukaryotic lineage very early in evolution. IMAGES:

人类复制蛋白A（Human replication protein A, RP-A）是一种三亚基蛋白，为体外实验中猿猴病毒40（simian virus 40, SV40）的复制所必需。RP-A的锥虫同源物已从簇生短膜虫（Crithidia fasciculata）中纯化得到，该复合物由分子量分别为51 kDa、28 kDa与14 kDa的三种多肽以1:1:1的摩尔比组成，可通过其大亚基结合单链DNA，并定位于细胞核内。簇生短膜虫RP-A在依赖大T抗原的SV40复制起点解旋反应中，可替代人类RP-A行使功能，同时能够促进人类DNA聚合酶α/引物酶介导的DNA合成与引物生成，但无法在体外有效支持SV40的DNA复制过程。人类与锥虫RP-A在结构与功能上的这种高度保守性提示，在进化早期便从真核生物主干谱系分化的各类生物中，DNA复制的起始与延伸层面的机制均存在保守性。图像：