The small terminase, gp16, of bacteriophage T4 is a regulator of the DNA packaging motor.
Tailed bacteriophages and herpes viruses use powerful molecular motors to translocate DNA into a preassembled prohead and compact the DNA to near crystalline density. The phage T4 motor, a pentamer of 70-kDa large terminase, gp17, is the fastest and most powerful motor reported to date. gp17 has an ATPase activity that powers DNA translocation and a nuclease activity that cuts concatemeric DNA and generates the termini of viral genome. An 18-kDa small terminase, gp16, is also essential, but its role in DNA packaging is poorly understood. gp16 forms oligomers, most likely octamers, exhibits no enzymatic activities, but stimulates the gp17-ATPase activity, and inhibits the nuclease activity. Extensive mutational and biochemical analyses show that gp16 contains three domains, a central oligomerization domain, and N- and C-terminal domains that are essential for ATPase stimulation. Stimulation occurs not by nucleotide exchange or enhanced ATP binding but by triggering hydrolysis of gp17-bound ATP, a mechanism reminiscent of GTPase-activating proteins. gp16 does not have an arginine finger but its interaction with gp17 seems to position a gp17 arginine finger into the catalytic pocket. gp16 inhibits DNA translocation when gp17 is associated with the prohead. gp16 restricts gp17-nuclease such that the putative packaging initiation cut is made but random cutting is inhibited. These results suggest that the phage T4 packaging machine consists of a motor (gp17) and a regulator (gp16). The gp16 regulator is essential to coordinate the gp17 motor ATPase, translocase, and nuclease activities, otherwise it could be suicidal to the virus.
Al-Zahrani
Abdulrahman S
AS
Department of Biology, The Catholic University of America, Washington, D. C. 20064, USA.
Kondabagil
Kiran
K
Gao
Song
S
Kelly
Noreen
N
Ghosh-Kumar
Manjira
M
Rao
Venigalla B
VB
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D017122:Bacteriophage T4 / Q000502:physiology*; D004279:DNA, Viral / Q000235:genetics / Q000378:metabolism*; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000378:metabolism*; D006868:Hydrolysis; D055503:Protein Multimerization / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000502:physiology; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D019065:Virus Assembly / Q000502:physiology*
D004279:DNA, Viral; D014764:Viral Proteins; C065038:gp17 protein, Enterobacteria phage T4; D000255:Adenosine Triphosphate; D004706:Endodeoxyribonucleases; C104812:terminase, phage T4; D000251:Adenosine Triphosphatases