Bernstein J A, Richardson C C
Department of Biological Chemistry, Harvard Medical School, Boston, MA 02115.
Proc Natl Acad Sci U S A. 1988 Jan;85(2):396-400. doi: 10.1073/pnas.85.2.396.
Bacteriophage T7 gene 4 protein, purified from phage-infected cells, consists of a mixture of 56- and 63-kDa species that provides helicase and primase activities required for T7 DNA replication. The 56-kDa species has been purified independently of the colinear 63-kDa species. Like a mixture of the two proteins, the 56-kDa protein binds single-stranded DNA in the presence of dTTP, catalyzes DNA-dependent hydrolysis of dTTP, and has helicase activity. In contrast to the mixture, the 56-kDa protein cannot catalyze template-dependent RNA primer synthesis. In the absence of a DNA template, both the 56-kDa protein and the mixture of the two species synthesize low levels of diribonucleotide. A putative "zinc finger" present near the amino terminus of the 63-kDa protein but absent from the 56-kDa protein may play a major role in the recognition of primase sites in the template.
从噬菌体感染的细胞中纯化得到的噬菌体T7基因4蛋白，由56 kDa和63 kDa两种蛋白组成的混合物构成，该混合物提供了T7 DNA复制所需的解旋酶和引发酶活性。56 kDa的蛋白已独立于共线性的63 kDa蛋白进行了纯化。与两种蛋白的混合物一样，56 kDa的蛋白在dTTP存在的情况下结合单链DNA，催化dTTP的DNA依赖性水解，并具有解旋酶活性。与混合物不同的是，56 kDa的蛋白不能催化模板依赖性RNA引物的合成。在没有DNA模板的情况下，56 kDa的蛋白和两种蛋白的混合物都能合成低水平的二核苷酸。63 kDa蛋白氨基末端附近存在一个假定的“锌指”，而56 kDa蛋白中不存在，它可能在识别模板中的引发酶位点方面起主要作用。
