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J. Biol. Chem., Vol. 279, Issue 39, 40795-40801, September 24, 2004

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The Functional Domains of Bacteriophage T4 Terminase^*

Shuji Kanamaru¶, Kiran Kondabagil||, Michael G. Rossmann**, and Venigalla B. Rao, Supported by National Science Foundation Grant MCB-0110574||

From the ^||Department of Biology, The Catholic University of America, Washington, D. C. 20064 and the Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907

The packaging of double-stranded genomic DNA into some viral and all bacteriophage capsids is driven by powerful molecular motors. In bacteriophage T4, the motor consists of the portal protein assembly composed of twelve copies of gene product 20 (gp20, 61 kDa) and an oligomeric terminase complex composed of gp16 (18 kDa) and gp17 (70 kDa). The packaging motor drives the 171-kbp T4 DNA into the capsid utilizing the free energy of ATP hydrolysis. Evidence suggests that gp17 is the key component of the motor; it exhibits ATPase, nuclease, and in vitro DNA-packaging activities. The N- and C-terminal halves of gp17 were expressed and purified to homogeneity and found to have ATPase and nuclease activities, respectively. The N-terminal domain exhibited 2–3-fold higher K_cat values for gp16-stimulated ATPase than the full-length gp17. Neither of the domains, individually or together, exhibited in vitro DNA-packaging activity, suggesting that communication between the domains is essential for DNA packaging. The domains, in particular the C-terminal domain or a mixture of both the N- and C-terminal domains, inhibited in vitro DNA packaging that is catalyzed by full-length gp17. In conjunction with genetic evidence, these data suggest that the domains compete with the full-length gp17 for binding sites on the portal protein. A model for the assembly of the T4 DNA-packaging machine is presented.

Received for publication, April 1, 2004 , and in revised form, June 24, 2004.

^* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Both authors contributed equally to and share first authorship for this work.

^¶ Present address: Dept. of Biomolecular Engineering, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-Ru, Yokohama 226-8501, Japan.

^** Supported by National Science Foundation Grant MCB-9986266.

To whom correspondence should be addressed: Dept. of Biology, 103 McCort Ward Hall, The Catholic University of America, 620 Michigan Ave., N.E., Washington, DC 20064. Tel.: 202-319-5271; Fax: 202-319-6161; E-mail: rao{at}cua.edu.

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