Identification of a simian immunodeficiency virus reverse transcriptase variant with enhanced replicational fidelity in the late stage of viral infection.

Genomic hypermutation of human and simian immunodeficiency viruses (HIV and SIV) enables these viruses to adapt and escape from various types of anti-viral selection by altering the molecular properties of viral gene products. In this study, we examined whether the biochemical and catalytic properties of SIV DNA polymerases (reverse transcriptases; RT) can change during the course of viral infection. For this test, we analyzed RTs obtained from two SIV clones, SIVMNE CL8 and SIVMNE 170. SIVMNE 170 was isolated during the late symptomatic phase of infection with the parental strain, SIVMNE CL8. We found these two RTs have identical DNA polymerase specific activities and kinetics with three different DNA and RNA templates. In addition, the processivity of these two SIV RT proteins were also similar. However, as demonstrated by a misincorporation assay, the SIVMNE 170 RT showed much higher fidelity than SIVMNE CL8. The fidelity difference between these two SIV RTs was also confirmed by a steady state kinetic fidelity assay. These findings suggest that the fidelity of lentiviral RTs may change during the course of viral infection, possibly in response to alterations of host anti-viral immune capability. In addition, our sequence analysis of these two RT genes proposes possible structural strategies that the virus may employ to alter RT fidelity.