Kolodner R, Richardson C C
Proc Natl Acad Sci U S A. 1977 Apr;74(4):1525-9. doi: 10.1073/pnas.74.4.1525.
Homogeneous preparations of phage T7 gene 4 protein catalyze the hydrolysis of dNTPs and rNTPs to NDPs and Pi in the presence of single-stranded DNA. Synthesis on single-stranded DNA by T7 DNA polymerase (DNA nucleotidyltransferase; deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7) does not affect the hydrolysis of NTPs by the gene 4 protein. Gene 4 protein does not catalyze the hydrolysis of NTPs in the presence of duplex DNA, nor can T7 DNA polymerase use duplex DNA as a template. However, the two proteins together can replicate duplex DNA and, under these conditions, synthesis is accompanied by hydrolysis of NTPs. During synthesis on duplex templates in the presence of T7 DNA polymerase, gene 4 protein, dNTPs, and rNTPs, 4.2 NTPs are hydrolyzed for each dNMP polymerized. 2'3'-Dideoxy-TTP, an inhibitor of DNA synthesis, inhibits hydrolysis by the gene 4 protein during synthesis on duplex DNA, and beta, gamma-methylene-dTTP, an inhibitor of hydrolysis by the gene 4 protein, stops DNA synthesis on duplex DNA. The multiple activities of gene 4 protein are shown to reside in a single protein molecule.
噬菌体T7基因4蛋白的均一制剂在单链DNA存在的情况下催化dNTP和rNTP水解为NDP和磷酸。T7 DNA聚合酶（DNA核苷酸转移酶；脱氧核苷三磷酸：DNA脱氧核苷酸转移酶，EC 2.7.7.7）在单链DNA上的合成不影响基因4蛋白对NTP的水解。基因4蛋白在双链DNA存在时不催化NTP的水解，T7 DNA聚合酶也不能将双链DNA用作模板。然而，这两种蛋白质一起可以复制双链DNA，在这些条件下，合成伴随着NTP的水解。在T7 DNA聚合酶、基因4蛋白、dNTP和rNTP存在的情况下，在双链模板上合成时，每聚合一个dNMP会水解4.2个NTP。DNA合成抑制剂2'3'-二脱氧-TTP在双链DNA合成过程中抑制基因4蛋白的水解，而基因4蛋白水解抑制剂β，γ-亚甲基-dTTP则阻止双链DNA上的DNA合成。基因4蛋白的多种活性被证明存在于单个蛋白质分子中。
