title: Topography of a flexible ribonucleoprotein helix: protein-protein contacts in Sendai virus nucleocapsids.
abstract: Contacts among the three polypeptide species in the flexible helical nucleocapsids of a paramyxovirus were examined with bifunctional protein cross-linking reagents. Polypeptides L and P, minor components of Sendai virus nucleocapsids implicated in viral RNA polymerase activity, were efficiently cross-linked into large complexes, indicating that they enjoy abundant contacts with neighboring protein molecules in the helix. Less reactivity was found in the case of the major structural polypeptide, NP; about half of all molecules of NP formed large cross-linked complexes, most of the rest remaining as monomers along with a small proportion of homodimers and low-order oligomers. Marked heterogeneity in the cross-linking reactivity of NP molecules, which may reflect the conformational quasi-equivalence inherent in a flexible helix, was indicated by the production of several conformers of homodimers and other low-order oligomers of NP, and by failure of the kinetics of NP cross-linking to conform to a simple statistical model of random polmerization. The validity of the statistical model was shown by cross-linking experiments with the rigid helical virus, tobacco mosaic virus.
mesh_terms: D002213:Capsid / Q000378:metabolism*; D004120:Dimethyl Suberimidate / Q000494:pharmacology; D008970:Molecular Weight; D010222:Parainfluenza Virus 1, Human / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D010455:Peptides / Q000032:analysis / Q000378:metabolism; D011487:Protein Conformation; D012367:RNA, Viral; D014764:Viral Proteins / Q000032:analysis / Q000378:metabolism
chemical_list: D010455:Peptides; D012367:RNA, Viral; D014764:Viral Proteins; D004120:Dimethyl Suberimidate