J Gen Virol 32 (1976), 413-430; DOI 10.1099/0022-1317-32-3-413
© 1976 Society for General Microbiology
RNA Polymerase Components in Semliki Forest Virus-Infected Cells: Synthesis from Large Precursors
J. C. S. Clegg,
H. Brzeski and
S. I. T. Kennedy
Department of Biological Sciences, University of Warwick, Coventry, Warwickshire CV4 7AL
Two previously undescribed stable polypeptides (referred to as nsp 90 and nsp 63) appear in mammalian and avian cells infected with Semliki Forest virus. They are distinguishable from the virus structural proteins and their known precursors by their molecular weights and tryptic peptide maps, and are identical in size to two polypeptides found in purified preparations of virus-specific RNA polymerase. Data from pulse-chase experiments and from the use of inhibitors of proteolytic cleavage indicate that nsp 90 and nsp 63 are synthesized via a series of post-translational cleavages from three larger polypeptides, p200, p184 and p150. The labelling kinetics after synchronous initiation of protein synthesis are also consistent with the synthesis of nsp 90 and nsp 63 from a common initiation site, and show that nsp 63 is located close to this site. It is concluded that nsp 90 and nsp 63 are components of the virus-specific RNA polymerase, and are synthesized via a post-translational cleavage scheme entirely separate from that leading to the synthesis of the virus structural proteins.
Received 18 February 1976;
accepted 23 April 1976.
Copyright © 1976 by the Society for General Microbiology.
