FELINE IMMUNODEFICIENCY VIRUS REVERSE-TRANSCRIPTASE - EXPRESSION, FUNCTIONAL-CHARACTERIZATION, AND RECONSTITUTION OF THE 66- AND 51-KILODALTON SUBUNITS

The two subunits of the feline immunodeficiency virus (FIV) reverse tr anscriptase (RT) were cloned and functionally expressed in Escherichia coli. The recombinant proteins are enzymatically active as homodimers (p66 and p51) as well as a heterodimer p66/p51. The biochemical prope rties of the FIV RT are very similar to those of the counterpart of th e human immunodeficiency virus type 1 in being an RNA-dependent and DN A-dependent DNA polymerase. When a double-stranded DNA containing a sm all gap of 26 nucleotides was tested, we found a new activity of the F IV RT p66/p51 heterodimer-the cat viral enzyme could perform strand di splacement DNA synthesis of approximately 300 bases. The FIV RT homodi mer p66 alone could carry out limited strand displacement DNA synthesi s, but this activity was stimulated by the p51 subunit at a molar rati o of one molecule of p66 to five molecules of p51. On the other hand, the homodimeric p51 itself was unable to fill a small gap of 26 nucleo tides in a double-stranded DNA substrate and was not active by itself in strand displacement DNA synthesis. These data are in agreement with an earlier finding of strand displacement DNA synthesis by human immu nodeficiency virus type 1 RT (M. Hottiger, V. N. Podust, R. L. Thimmig , C. S. McHenry, and U. Hiibscher. J. Biol. Chem, 269:986-991, 1994). Our data therefore suggest a general and important function of lentivi ral p51 subunits in strand displacement DNA synthesis which appears to be required in later stages of the lentiviral replication cycle, when DNA-dependent DNA synthesis occurs on double-stranded DNA.