Yan H, Chen C Y, Kobayashi R, Newport J
Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
Nat Genet. 1998 Aug;19(4):375-8. doi: 10.1038/1263.
The initiation of DNA replication involves a minimum of four factors: a specific DNA sequence (origin), an initiator protein which binds to the origin, a helicase that unwinds the origin and a protein that binds single-stranded DNA that stabilizes the unwound origin. In eukaryotic cells, the origin recognition complex (ORC) is the initiator protein and replication protein A (RPA; ref. 3) is the single-stranded DNA-binding protein. However, the helicase has not been identified and the nature of origins remains elusive, except in the case of Saccharomyces cerevisiae. A unique feature of eukaryotic DNA replication is that it occurs at a few-hundred discrete foci. It has thus been proposed that a real origin must contain a specific DNA sequence and must be attached to replication foci. Using Xenopus laevis egg extracts, we have identified and purified a 170-kD protein, focus-forming activity 1 (FFA-1), which is required for the formation of replication foci. Here we report that FFA-1 has DNA-helicase activity. Moreover, it is a homologue of the human Werner syndrome gene product WRN, a protein associated with premature ageing in humans.
DNA复制的起始至少涉及四个因素：特定的DNA序列（起始点）、与起始点结合的起始蛋白、解开起始点的解旋酶以及结合单链DNA以稳定解旋后的起始点的蛋白。在真核细胞中，起始识别复合物（ORC）是起始蛋白，复制蛋白A（RPA；参考文献3）是单链DNA结合蛋白。然而，除了酿酒酵母的情况外，解旋酶尚未被鉴定出来，起始点的性质仍然难以捉摸。真核DNA复制的一个独特特征是它发生在几百个离散的位点。因此有人提出，真正的起始点必须包含特定的DNA序列，并且必须附着在复制位点上。利用非洲爪蟾卵提取物，我们鉴定并纯化了一种170-kD的蛋白，即位点形成活性蛋白1（FFA-1），它是复制位点形成所必需的。在此我们报道FFA-1具有DNA解旋酶活性。此外，它是人类沃纳综合征基因产物WRN的同源物，WRN是一种与人类早衰相关的蛋白。
