HNH proteins are a widespread component of phage DNA packaging machines.
The genome packaging reactions of tailed bacteriophages and herpes viruses require the activity of a terminase enzyme, which is comprised of large and small subunits. Phage genomes are replicated as linear concatemers composed of multiple copies of the genome joined end to end. As the terminase enzyme packages the genome into the phage capsid, it cleaves the DNA into single genome-length units. In this work, we show that the phage HK97 HNH protein, gp74, is required for the specific endonuclease activity of HK97 terminase and is essential for phage head morphogenesis. HNH proteins are a very common family of proteins generally associated with nuclease activity that are found in all kingdoms of life. We show that the activity of gp74 in terminase-mediated cleavage of the phage cos site relies on the presence of an HNH motif active-site residue, and that the large subunit of HK97 terminase physically interacts with gp74. Bioinformatic analysis reveals that the role of HNH proteins in terminase function is widespread among long-tailed phages and is uniquely required for the activity of the Terminase_1 family of large terminase proteins.
Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, ON, Canada M5S 3E1.
Smriti
S
Kala
Nichole
N
Cumby
Paul D
PD
Sadowski
Batool Zafar
BZ
Hyder
Voula
V
Kanelis
Alan R
AR
Davidson
Karen L
KL
Maxwell
D000595:Amino Acid Sequence; D001435:Bacteriophages / Q000502:physiology* / Q000648:ultrastructure; D020134:Catalytic Domain; D002942:Circular Dichroism; D042003:DNA Packaging; D004706:Endodeoxyribonucleases / Q000378:metabolism; D004926:Escherichia coli / Q000821:virology; D006639:Histidine / Q000378:metabolism; D008969:Molecular Sequence Data; D011485:Protein Binding; D021122:Protein Subunits / Q000378:metabolism; D014764:Viral Proteins / Q000737:chemistry / Q000378:metabolism*; D019065:Virus Assembly
D021122:Protein Subunits; D014764:Viral Proteins; D006639:Histidine; D004706:Endodeoxyribonucleases; C030894:terminase
HNH endonuclease; bacteriophage HK97; molecular chaperone