Effect of supraoptimal temperatures upon tobacco mosaic virus RNA replicase

An examination of the effect of supraoptimal temperatures upon tobacco mosaic virus (TMV) RNA replicase demonstrated that the enzyme activity rapidly decreased at 40 degrees whether incubated in vitro after extraction or in leaves at that temperature prior to extraction and assay. The loss of replicase activity paralled the decline in capacity for in vivo incorporation of 32P into TMV RNA at 25 degrees following different periods of incubation at 40 degrews. The optimal temperature for replicase activity in vitro 35 degrees, and greater activity occurred at 40 than at 25 degrees. After about 15 min incubation at 40 degrees, in vivo incorporation of 32P into double-stranded TMV RNA became temperature-sensitive. This function could not be reproduced with the in vitro replicase system.