The optimal temperature for for MMLV is 42 degrees C. The optimal temperature for SuperScript II RT is 42 degrees C, and can be used up to 50 degrees C. The optimal temperature for SuperScript III RT is 50 degrees C, and can be used up to 55 degrees C. For some qRT-PCR reactions where gene-specific primers are used, you can do the RT reaction at 60 degrees C. The optimal temperature for SuperScript IV RT is 50 degrees C, but can be used up to 65 degrees C.