Order of transcription of genes of vesicular stomatitis virus

Abstract

The effect of ultraviolet radiation on the expression of the genes of vesicular stomatitis virus (VSV) was studied in a cell free system which executed coupled transcription and translation of the viral genes. In this system, which contained detergent activated virus and a cytoplasmic extract of mouse L cells, three of the five viral proteins (N, NS and M) were synthesized accurately and efficiently; a putative precursor to the viral glycoprotein (G) was also made, but synthesis of the L protein was not detected. In response to irradiation of VSV the synthesis of each protein in the coupled system displayed a characteristic single hit inhibition. This permitted calculation of the apparent target sizes for expression of the different viral genes relative to the entire genome (3.6 to 4.0 x 106 daltons) as measured by loss of infectivity. These are: N, 0.55 x 106; NS, 0.83 x 106; M 1.12 x 106; G, 1.76 x 106 daltons of RNA. Only the N protein gene has a target size which corresponds to that predicted from the molecular weight of its messenger RNA (molecular weight: 0.55 x 106). The target sizes for the other three genes are two to four times larger than expected and are not proportional to the molecular weights of their corresponding messenger RNAs (molecular weights: NS, 0.28 x 106; M, 0.28 x 106; G, 0.7 x 106). This polar effect of UV irradiation is inconsistent with independent transcription of each of the genes of VSV. Rather, the target sizes appear to be cumulative, suggesting that transcription initiates at a single point on VSV RNA and proceeds in the order 3' N NS M G (L) 5'.