Supramolecular organization of immature and mature murine leukemia virus revealed by electron cryo-microscopy: implications for retroviral assembly mechanisms.
We have used electron cryo-microscopy and image analysis to examine the native structure of immature, protease-deficient (PR-) and mature, wild-type (WT) Moloney murine leukemia virus (MuLV). Maturational cleavage of the Gag polyprotein by the viral protease is associated with striking morphological changes. The PR- MuLV particles exhibit a rounded central core, which has a characteristic track-like shell on its surface, whereas the WT MuLV cores display a polygonal surface with loss of the track-like feature. The pleomorphic shape and inability to refine unique orientation angles suggest that neither the PR- nor the WT MuLV adheres to strict icosahedral symmetry. Nevertheless, the PR- MuLV particles do exhibit paracrystalline order with a spacing between Gag molecules of approximately 45 A and a length of approximately 200 A. Because of the pleomorphic shape and paracrystalline packing of the Gag-RNA complexes, we raise the possibility that assembly of MuLV is driven by protein-RNA, as well as protein-protein, interactions. The maturation process involves a dramatic reorganization of the packing arrangements within the ribonucleoprotein core with disordering and loosening of the individual protein components.
Yeager
M
M
Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA. yeager@scripps.edu
Wilson-Kubalek
E M
EM
Weiner
S G
SG
Brown
P O
PO
Rein
A
A
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D010450:Endopeptidases / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D008958:Models, Molecular; D008979:Moloney murine leukemia virus / Q000201:enzymology / Q000502:physiology* / Q000648:ultrastructure; D019065:Virus Assembly
D010450:Endopeptidases