Optimal conditions for synthesis of long complementary DNA product with Moloney murine leukemia virus

The role of template-primer in protection of reverse transcriptase from thermal inactivation

We compared the thermal stabilities of wild-type recombinant avian myeloblastosis virus (AMV) and Moloney murine leukemia virus (M-MLV) reverse transcriptase (RT) with those of mutants of the recombinant enzymes lacking RNase H activity. They differed in resistance to thermal inactivation at elevated temperatures in the presence of an RNA/DNA template-primer. RNase H-minus RTs retained the ability to efficiently synthesize cDNA at much higher temperatures. We show that the structure of the template-primer has a critical bearing on protection of RT from thermal inactivation. RT RNase H activity rapidly alters the structure of the template-primer to forms less tightly bound by RT and thus less able to protect the enzyme at elevated temperatures. We also found that when comparing wild-type or mutant AMV RT with the respective M-MLV RT, the avian enzymes retained more DNA synthetic activity at elevated temperatures than murine RTs. Enzyme, template-primer interaction again played the most significant role in producing these differences. AMV RT binds much tighter to template- primer and has a much greater tendency to remain bound during cDNA synthesis than M-MLV RT and therefore is better protected from heat inactivation.

Manganese cations increase the mutation rate of human immunodeficiency virus type 1 ex vivo

Human immunodeficiency virus (HIV) reverse transcription is an error-prone process with an overall mutation rate of approximately 3.4 x 10(-5) per base per replication cycle. This rate can be modulated by changes in different components of the retrotranscription reaction. In particular, in vitro substitution of magnesium cations (Mg2+) by manganese cations (Mn2+) has been shown to increase misincorporation of deoxynucleotide triphosphates (dNTPs) and to alter substrate specificity. Here, it is shown that Mn2+ also increases the HIV mutation rate ex vivo. Treatment of permissive cells with Mn2+ and subsequent HIV infection resulted in at least 6-fold and 10-fold increases in the mutant and mutation frequencies respectively, thus illustrating a further example of how to influence HIV genetic variation.