INTERFERENCE WITH VIRAL-INFECTION BY RNA REPLICASE DELETED AT THE CARBOXY-TERMINAL REGION

Escherichia coli cells harboring an altered Qβ RNA replicase which has amino acid substitutions of the glycine residue at position 357 in the conserved sequence Tyr356-Gly357-Asp358-Asp359of the β-subunit protein lost the replicase activity but interfered with proliferation of Qβ phage [Inokuchi and Hirashima (1987) J. Virol. 61, 3946-3949]. To examine the mechanism of the interference, we further analyzed various mutants lacking the carboxy-terminal region of the β-subunit protein. The cells expressing the β-subunit gene with up to 17% deletion from the carboxy-terminus of the protein prevented the proliferation of Qβ phage. However, in the case that the deletion extended beyond 25% from the carboxy-terminus, the cells showed no interference. In addition, when the interference took place, the phage coat protein synthesis was inhibited. These results indicate that the region between amino acids 440 and 487 of the β-subunit protein is involved in the interference and suggest that the defective replicase inhibits the phage coat protein synthesis by competing with the ribosomes at the initiation site of the coat gene. © 1990 Copyright, 1990 by the Journal of Biochemistry.