BIGSS – BioMedTec Internationational Graduate School of Science

Foamy viruses belong to the retroviridae and follow a replication pattern unique among retroviruses: (a) reverse transcription occurs before the virus leaves the host cell, (b) the pol-gene is expressed from a separate mRNA and (c) the viral protease is not cleaved off the Pol-polyprotein. Thus the reverse transcriptase (PR-RT) harbors a protease, polymerase and RNase H domain.

We purified a recombinant PR-RT and analyzed its enzyme activities. Our results show that SFV-1 PR-RT exhibits RNase H and polymerase activities, however it is less processive than HIV-1 RT. Although the enzyme is monomeric in size exclusion chromatography, the PR domain harbors proteolytic activity. Since retroviral aspartate proteases have been shown to be dimers, dimerization might occur upon substrate binding. Furthermore, we could demonstrate that a truncated version of the protease domain expressed separately, is active. The determination of the protease structure by NMR spectroscopy is in progress.

The only known drug that effectively inhibits SFV-1 reverse transcriptase in vivo is azidothymidine (AZT). Mutations conferring resistance to AZT are located within the RT gene. To determine the mechanism of AZT resistance, we cloned and purified the recombinant AZT-resistant PR-RT.