The 35-kDa protein from the N-terminus of the potyviral polyprotein functions as a third virus-encoded proteinase.
The polyprotein encoded by plant potyviruses is proteolytically processed to at least eight mature products by viral-encoded proteinases. While the proteinases that catalyze processing at most of the cleavage sites have been identified, the enzyme responsible for cleavage between the 35-kDa protein and helper component-proteinase (HC-Pro), near the N-terminus of the viral polyprotein, has not been mapped or characterized previously. Polyproteins containing the 35-kDa protein and HC-Pro were synthesized in the wheat germ system using defined RNA transcripts and were demonstrated to undergo proteolysis to generate products that resemble fully processed proteins. The C-terminal half of the 35-kDa protein was found to be required for proteolysis, whereas most of the HC-Pro sequence was dispensable. Amino acid substitutions affecting three positions, each of which are conserved in the 35-kDa protein encoded by five potyviruses, were shown to inhibit protein processing. These data suggest that the 35-kDa protein functions as a proteinase to cleave at its C-terminus. A model that accounts for all proteolytic processing events in the potyviral polyprotein is presented.
Verchot
J
J
Department of Biology, Texas A&M University, College Station 77843.
Koonin
E V
EV
Carrington
J C
JC
D000595:Amino Acid Sequence; D002474:Cell-Free System; D010450:Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010942:Plant Viruses / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D010944:Plants / Q000382:microbiology; D010957:Plasmids / Q000235:genetics; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D012367:RNA, Viral / Q000378:metabolism; D016415:Sequence Alignment; D014764:Viral Proteins / Q000737:chemistry / Q000378:metabolism*
C071896:35-kDa protein, Potyvirus; D012367:RNA, Viral; D014764:Viral Proteins; D010450:Endopeptidases