There are mutated or modified forms of reverse transcriptases so that these enzymes have optimal properties and activities different from the native forms of reverse transcriptase (MMLV or AMV). These modified reverse transcriptases have the same primary function as the native forms: an RNA-dependent DNA polymerase which synthesizes the first complementary DNA strand (cDNA) from a single-stranded RNA template to which a primer has been hybridized.

For example, changes may be made in RNase H domain of the reverse transcriptase in order to suppress its activity. The absence of RNase H activity makes it possible to eliminate the degradation of the RNA during the synthesis of the cDNA strand, resulting in a higher amount and length of the synthesized cDNA.

Other modifications may include the fidelity of the reverse transcriptase or its ability to synthesize cDNA from RNA rich in GC. For this latter parameter, reverse transcriptase is capable of functioning at lower temperatures in order to avoid the formation of frequent secondary structures with the GC-rich RNAs.