Rinderpest virus is a morbillivirus and the causative agent of an important disease of cattle and wild bovids. The P genes of all morbilliviruses give rise to two
proteins in addition to the P
protein itself: use of an alternate start translation site, in a second open reading frame, gives rise to the C
protein, while cotranscriptional insertion of an extra base gives rise to the V
protein, a fusion of the amino-terminal half of P to a short, highly conserved,
cysteine-rich
zinc binding domain. Little is known about the function of either of these two
proteins in the rinderpest virus life cycle. We have constructed recombinant
rinderpest viruses in which the expression of these
proteins has been suppressed, individually and together, and studied the replication of these viruses in tissue culture. We show that the absence of the V
protein has little effect on the replication rate of the virus but does lead to an increase in synthesis of genome and antigenome RNAs and a change in cytopathic effect to a more syncytium-forming phenotype. Virus that does not express the C
protein, on the other hand, is clearly defective in growth in all cell lines tested, and this defect appears to be related to a decreased transcription of
mRNA from viral genes. The phenotypes of both individual mutant virus types are both expressed in the double mutant expressing neither V nor C.