Identification of a new protein present in vesicular stomatitis virus-infected Chinese hamster ovary cells as a degradation product of viral M protein.

In addition to the five previously described vesicular stomatitis virus (VSV) proteins (L, G, N, NS, and M), a protein (Mr 17,500) accumulated late in infection of Chinese hamster ovary cells. The protein, designated M', was a cleavage product of the viral M protein (Mr 26,000) both in vivo and in vitro. (a) M' was precipitated by anti VSV serum, indicating that it is of viral origin. (b) M' peptides generated using Staphylococcus V8 protease or chymotrypsin were shared by M, but not by the other VSV proteins. (c) The conversion of M to M' was enzymatic. The enzyme denoted M protease was heat labile, was inhibited by the serine protease inhibitor phenylmethylsulfonyl fluoride, and its accumulation, which commenced between 2 and 3 hr after infection, required protein synthesis. (d) The amounts of L, G, N, and NS increased in CHO-infected cells while the amount of M increased for only 3-4 hr and decreased thereafter. Since M has been implicated in the inhibition of VSV transcription, it is possible that regulation of the amount of M by degradation is important in the regulation of VSV transcription.