Induction of particle polymorphism by cucumber necrosis virus coat protein mutants in vivo.
The Cucumber necrosis virus (CNV) particle is a T=3 icosahedron consisting of 180 identical coat protein (CP) subunits. Plants infected with wild-type CNV accumulate a high number of T=3 particles, but other particle forms have not been observed. Particle polymorphism in several T=3 icosahedral viruses has been observed in vitro following the removal of an extended N-terminal region of the CP subunit. In the case of CNV, we have recently described the structure of T=1 particles that accumulate in planta during infection by a CNV mutant (R1+2) in which a large portion of the N-terminal RNA binding domain (R-domain) has been deleted. In this report we further describe properties of this mutant and other CP mutants that produce polymorphic particles. The T=1 particles produced by R1+2 mutants were found to encapsidate a 1.9-kb RNA species as well as smaller RNA species that are similar to previously described CNV defective interfering RNAs. Other R-domain mutants were found to encapsidate a range of specifically sized less-than-full-length CNV RNAs. Mutation of a conserved proline residue in the arm domain near its junction with the shell domain also influenced T=1 particle formation. The proportion of polymorphic particles increased when the mutation was incorporated into R-domain deletion mutants. Our results suggest that both the R-domain and the arm play important roles in the formation of T=3 particles. In addition, the encapsidation of specific CNV RNA species by individual mutants indicates that the R-domain plays a role in the nature of CNV RNA encapsidated in particles.
Kakani
Kishore
K
Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, 4200 Hwy. 97, Box 5000, Summerland, British Columbia, Canada.
Reade
Ron
R
Katpally
Umesh
U
Smith
Thomas
T
Rochon
D'Ann
D
D036022:Capsid Proteins / Q000235:genetics*; D004587:Electrophoresis, Agar Gel; D046529:Microscopy, Electron, Transmission; D050505:Mutant Proteins / Q000235:genetics; D012367:RNA, Viral / Q000235:genetics* / Q000302:isolation & purification; D017864:Tombusvirus / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure*; D014771:Virion / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure*
D036022:Capsid Proteins; D050505:Mutant Proteins; D012367:RNA, Viral