Normal Replication of Vesicular Stomatitis Virus without C Proteins

The expression of two small basic proteins (C and C′) encoded by a second open reading frame of the New Jersey serotype of vesicular stomatitis virus (VSV) P gene was reported previously (Spiropoulou and Nichol,J. Virol.,67, 3103–3110, 1993). Here we found that the Indiana serotype virus also expressed C and C′ proteins from this reading frame. We eliminated C and C′ expression by making a single base change that introduced a stop codon in the C and C′ coding sequence, but left the P-protein sequence unchanged. This mutated P gene supported normal replication and packaging of VSV minigenomes encoding G and M proteins. The mutated P gene was also recombined into an infectious clone of VSV that was used to recover virus. The mutant virus no longer expressed the C and C′ proteins but showed growth kinetics identical to wild-type virus. The amounts of viral mRNAs and proteins synthesized were indistinguishable in mutant and wild-type virus infected cells as were the yields and composition of mutant and wild-type virus particles. The kinetics of host protein-synthesis shut-off were also identical for both viruses. Although the C and C′ proteins were dispensable for VSV growth in tissue culture, they are known to be conserved in all vesiculoviruses, and thus perhaps play a role in viral pathogenesis or transmission by insect vectors.