Effect of temperature-sensitive, replication-defective mutations on RNA synthesis of cowpea chlorotic mottle virus

The RNA synthesis of replication-deficient, temperature-sensitive mutants of cowpea chlorotic mottle virus (CCMV) with mutations on either RNA 1 or RNA 3 was examined in temperature shift experiments. Viral RNA synthesis by the mutants at 25 degrees was similar to that of wild-type CCMV, but upon shift to 35 degrees , synthesis of mutant virus RNAs declined over a 16-hr period in contrast to continued synthesis by wild-type CCMV. Continued RNA synthesis, though at a reduced level, by the mutants during the initial periods following the shift to 35 degrees demonstrated that the enzymes involved in viral RNA synthesis of the mutants continued activity after the shift to the nonpermissive temperature. There was no clear correlation between a specific, defect in viral RNA synthesis and whether the mutation occurred on either RNA 1 or RNA 3. New replicative complexes appeared not to be produced at 35 degrees suggesting that gene products from both RNA 1 and RNA 3 may function coordinately in the replication complex. One mutant produced a reduced ratio of RNA 3 that was exaggerated upon shift to the restrictive temperature.