A NEW CIS-ACTING ELEMENT FOR RNA REPLICATION WITHIN THE 5'-NONCODING REGION OF POLIOVIRUS TYPE-1 RNA

Mouse cells expressing the human poliovirus receptor (PVR-mouse cells) as well as human HeLa cells are susceptible to poliovirus type 1 Mahoney strain and produce a large amount of progeny virus at 37 degrees C. However, the virus yield is markedly reduced at 40 degrees C in PVR-mouse cells but not in HeLa cells. The reduction in virus yield at 40 degrees C appears to be due to a defective initiation process in positive strand RNA synthesis (K. Shiroki, H. Kato, S. Koike, T. Odaka, and A. Nomoto, J. Virol. 67:3989-3996, 1993). To gain insight into the molecular mechanisms involved in this detective process, naturally occurring heat-resistant (H-r)-mutants which show normal growth ability in PVR-mouse cells even at 40 degrees C were isolated from a virus stock of the Mahoney strain and their mutation sites that affect the phenotype were identified. The key mutation was a change from adenine (A) to guanine (G) at nucleotide position (nt) 133 within the 5' noncoding region of the RNA. This mutation also gave an H-r phenotype to the viral plus-strand RNA synthesis in PVR-mouse cells. Mutant Mahoney strains with a single point mutation at nt 133 (A to G, C, or T or deletion) were investigated for their ability to grow in PVR-mouse cells at 40 degrees C. Only the mutant carrying G at nt 133 showed an H-r growth phenotype in PVR-mouse cells. These results suggest that a host cellular factor(s) interacts with an RNA segment around nt 133 of the plus-strand RNA or the corresponding region of the minus-strand RNA, contributing to efficiency of plus-strand RNA synthesis.