Transcriptional map for Newcastle disease virus

Abstract

A transcriptional map of Newcastle disease virus was determined by measuring the kinetics of UV inactivation of the transcription of individual genes and of viral infectivity. The inactivation of single genes was monitored by measuring the reduction in the accumulation of viral gene products in vivo and in vitro. In vivo, the accumulation of viral polypeptides in infected cells was measured after reversal of a cycloheximide treatment designed to inhibit secondary transcription. Actinomycin D and a hypertonic medium were used to decrease selectively the synthesis of host cell polypeptides in infected cells. In vitro, mRNA's synthesized by irradiated viruses were analyzed by translation in cell-free systems under conditions in which the amount of each polypeptide synthesized reflected the relative abundance of the corresponding mRNA. UV target sizes were obtained for the genes coding for the HN, F0, NP, M, L, and P polypeptides; the 47,000-dalton protein was not detected. A comparison of the UV target sizes with the corresponding gene sizes suggested that transcription of these genes initiated at a single promotor and proceeded in the order NP, P, (F0, M), HN, L. These experiments were performed with Newcastle disease virus strains Australia-Victoria and B1-Hitchner; for both strains, two forms of the P polypeptide which differed in electrophoretic mobility were detected. Proof that the P protein is virus specific was obtained. In addition, infection of chicken embryo cells with avirulent strain B1-Hitchner enhanced the accumulation of at least four polypeptides that appeared to be specified by the host cell rather than by the infecting virus.