Temperature-sensitive polioviruses containing mutations in RNA polymerase

Abstract

Site-directed mutagenesis was performed to change the wild-type residue (asparagine) to aspartate, histidine, or tyrosine at amino acid 424 of the poliovirus RNA polymerase, 3D pol. The mutations were introduced into plasmids containing full-length viral cDNA and plasmids which direct the expression of 3D pol in Escherichia coli. Mutant viruses, recovered after transfection of HeLa cells with RNA transcripts of the full-length clones, produced small plaques at 32°. In addition, the plaquing efficiency was decreased for all three mutants at 37°, compared to 32°. The polyprotein processing of all mutant viruses was normal at the temperatures tested, suggesting that the mutant plaque phenotypes were not due to incorrect processing of viral proteins. Analyses of viral RNA synthesis in infected cells and of the polymerase activities of mutant enzymes produced in E. coli suggested the following: (1) The his 424, mutant enzyme appeared to be defective in the initiation of plus-strand RNA synthesis in HeLa cells. (2) The asp 424 mutant enzyme appeared unable to assume proper conformation for active polymerase function when synthesized at 37°. (3) The tyr 424 mutant enzyme was totally inactive when synthesized in E. coli at 37°.