Zhang, HuidongLee, Seung-JooKulczyk, Arkadiusz W.Zhu, BinRichardson, Charles C.2019-10-052012Zhang, Huidong, Seung-Joo Lee, Arkadiusz W. Kulczyk, Bin Zhu, and Charles C. Richardson. 2012. “Heterohexamer of 56- and 63-kDa Gene 4 Helicase-Primase of Bacteriophage T7 in DNA Replication.” Journal of Biological Chemistry 287 (41): 34273–87. https://doi.org/10.1074/jbc.m112.401158.0021-92581083-351Xhttp://nrs.harvard.edu/urn-3:HUL.InstRepos:41483344Bacteriophage T7 expresses two forms of gene 4 protein (gp4). The 63-kDa full-length gp4 contains both the helicase and primase domains. T7 phage also express a 56-kDa truncated gp4 lacking the zinc binding domain of the primase; the protein has helicase activity but no DNA-dependent primase activity. Although T7 phage grow better when both forms are present, the role of the 56-kDa gp4 is unknown. The two molecular weight forms oligomerize by virtue of the helicase domain to form heterohexamers. The 56-kDa gp4 and any mixture of 56- and 63-kDa gp4 show higher helicase activity in DNA unwinding and strand-displacement DNA synthesis than that observed for the 63-kDa gp4. However, single-molecule measurements show that heterohexamers have helicase activity similar to the 63-kDa gp4 hexamers. In oligomerization assays the 56-kDa gp4 and any mixture of the 56- and 63-kDa gp4 oligomerize to form more hexamers than does the 63-kDa gp4. The zinc binding domain of the 63-kDa gp4 interferes with hexamer formation, an inhibition that is relieved by the insertion of the 56-kDa species. Compared with the 63-kDa gp4, heterohexamers synthesize a reduced amount of oligoribonucleotides, mediated predominately by the 63-kDa subunits via a cis mode. During coordinated DNA synthesis 7% of the tetraribonucleotides synthesized are used as primers by both heterohexamers and hexamers of the 63-kDa gp4. Overall, an equimolar mixture of the two forms of gp4 shows the highest rate of DNA synthesis during coordinated DNA synthesis.en-USJournal Article2019-10-0510.1074/jbc.M112.401158