Generation and characterization of new highly thermostable and processive M-MuLV reverse transcriptase variants

In vitro synthesis of cDNA is one of the most important techniques in present molecular biology. Faithful synthesis of long cDNA on highly structured RNA templates requires thermostable and processive reverse transcriptases. In a recent attempt to increase the thermostability of the wt Moloney Murine leukemia virus reverse transcriptase (M-MuLV RT), we have employed the compartmentalized ribosome display (CRD) evolution in vitro technique and identified a large set of previously unknown mutations that enabled cDNA synthesis at elevated temperatures. In this study, we have characterized a group of the M-MuLV RT variants (28 novel amino acid positions, 84 point mutants) carrying the individual mutations. The performance of point mutants (thermal inactivation rate, substrate-binding affinity and processivity) correlated remarkably well with the mutation selection frequency in the CRD experiment. By combining the best-performing mutations D200N, L603W, T330P, L139P and E607K, we have generated highly processive and thermostable multiply-mutated M-MuLV RT variants. The processivity of the best-performing multiple mutant increased to 1500 nt (65-fold improvement in comparison to the wt enzyme), and the maximum temperature of the full-length 7.5-kb cDNA synthesis was raised to 62°C (17° higher in comparison with the wt enzyme).