Complementation of and interference with Sindbis virus replication by full-length and deleted forms of the nonstructural protein, nsP1, expressed in stable transfectants of Hela cells

Stable transfectants of Hela cells were isolated which expressed either the full-length 540-amino-acid Sindbis virus (SV) nonstructural protein, nsP1 (the form encoded by the mutant, SVLM21), or one of four forms with a carboxyl-terminal deletion. SVLM21, in contrast to standard SV (SVSTD), can replicate in Hela cells maintained in low-methionine (LM) medium. Expression of full-length nsP1(1-540), nsP1(1-492), or nsP1(1-448) resulted in complementation of SVSTD when infected Hela cells were kept in LM medium after infection. In contrast, when cells were infected with SVLM21 and maintained in LM medium, stable expression of any of the deleted forms of nsP1 interfered with the replication of virus. The ability of ''cellular'' nsP1 to complement SVSTD in LM medium correlated with its methyltransferase activity. (C) 1997 Academic Press