title: The functional domains of bacteriophage t4 terminase.
abstract: 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 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.
authors.affiliation: Department of Biology, The Catholic University of America, Washington, D. C. 20064, USA.
authors.forename: Shuji
authors.initials: S
authors.lastname: Kanamaru
authors.forename: Kiran
authors.initials: K
authors.lastname: Kondabagil
authors.forename: Michael G
authors.initials: MG
authors.lastname: Rossmann
authors.forename: Venigalla B
authors.initials: VB
authors.lastname: Rao
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D000595:Amino Acid Sequence; D017122:Bacteriophage T4 / Q000201:enzymology*; D004247:DNA / Q000737:chemistry; D004706:Endodeoxyribonucleases / Q000737:chemistry*; D004926:Escherichia coli / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014357:Trypsin / Q000494:pharmacology; D014764:Viral Proteins / Q000737:chemistry
chemical_list: D011994:Recombinant Proteins; D014764:Viral Proteins; C069680:bacteriophage T7 leg protein gp17; D000255:Adenosine Triphosphate; D004247:DNA; D004706:Endodeoxyribonucleases; C030894:terminase; D014357:Trypsin; D000251:Adenosine Triphosphatases