The Functional Domains of Bacteriophage T4 Terminase

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 Kcat 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 that the domains the full-length gp17 for the portal for the assembly of the T4 DNA-packaging is 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 Kcat 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 that the domains the full-length gp17 for the portal for the assembly of the T4 DNA-packaging is The packaging of double-stranded DNA into viral energy to and the packaging an that by to the T4 a double-stranded DNA to into a capsid the of the The In the of the the packaging motor 20 than that by for an the DNA-packaging the of the gene gene and and gene and and of bacteriophage T4, gp16 (18 kDa) and gp17 (70 the is the nuclease that the or of the In nuclease, and DNA to to the nuclease gp17. in the of the terminase to the DNA-packaging that a in the is the nuclease that the or of the In nuclease, and DNA to to the nuclease gp17. in the of the terminase to the DNA-packaging that a in the the of in the complex is In the of the terminase the viral it to the that is to the and it to the by the into the of the portal protein a of the the and DNA a of ATP of ATP for packaging of T4 DNA into the T4 the gp17 terminase a in the The terminase and the DNA the and gp17 exhibits ATPase and nuclease in the of the ATPase is and the packaging is The gp16 exhibits of activities. 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capsid The of in the of ATP energy and DNA packaging the of in the terminase that the T4 gp17 terminase consists of The purified N- and C-terminal halves of gp17 ATPase and terminase activities, that the in the full-length the of domains by an and domain the Neither of the domains, or together, in vitro DNA-packaging communication between the domains to the ATPase and nuclease the packaging the terminase for packaging DNA and that in the some of the by a in a of ATPase or terminase and of the terminase domains the key in the ATPase and nuclease DNA packaging. for the assembly of the T4 DNA-packaging is the of the is that gp16 an or a in a of gp17 a the of a of gp17 and by The and in and is in the a ATPase is the purified gp17. 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