Measles virus phosphoprotein gene products: conformational flexibility of the P/V protein amino-terminal domain and C protein infectivity factor function.
The measles virus (MV) P gene codes for three proteins: P, an essential polymerase cofactor, and V and C, which have multiple functions but are not strictly required for viral propagation in cultured cells. V shares the amino-terminal domain with P but has a zinc-binding carboxyl-terminal domain, whereas C is translated from an overlapping reading frame. During replication, the P protein binds incoming monomeric nucleocapsid (N) proteins with its amino-terminal domain and positions them for assembly into the nascent ribonucleocapsid. The P protein amino-terminal domain is natively unfolded; to probe its conformational flexibility, we fused it to the green fluorescent protein (GFP), thereby also silencing C protein expression. A recombinant virus (MV-GFP/P) expressing hybrid GFP/P and GFP/V proteins in place of standard P and V proteins and not expressing the C protein was rescued and produced normal ratios of mono-, bi-, and tricistronic RNAs, but its replication was slower than that of the parental virus. Thus, the P protein retained nearly intact polymerase cofactor function, even with a large domain added to its amino terminus. Having noted that titers of cell-associated and especially released MV-GFP/P were reduced and knowing that the C protein of the related Sendai virus has particle assembly and infectivity factor functions, we produced an MV-GFP/P derivative expressing C. Intracellular titers of this virus were almost completely restored, and those of released virus were partially restored. Thus, the MV C protein is an infectivity factor.
Devaux
Patricia
P
Molecular Medicine Program and Virology and Gene Therapy Graduate Track, Mayo Clinic College, Rochester, MN, USA.
Cattaneo
Roberto
R
D000818:Animals; D002522:Chlorocebus aethiops; D008459:Measles virus / Q000472:pathogenicity*; D010750:Phosphoproteins / Q000737:chemistry*; D011487:Protein Conformation; D014709:Vero Cells; D014764:Viral Proteins / Q000737:chemistry* / Q000502:physiology*; D014779:Virus Replication
C055859:P protein, Sendai virus; D010750:Phosphoproteins; C069181:V protein, measles virus; D014764:Viral Proteins