ALTERNATIVE MODES OF POLYMERIZATION DISTINGUISH THE SUBUNITS OF EQUINE INFECTIOUS-ANEMIA VIRUS REVERSE-TRANSCRIPTASE

A comparative study of recombinant 51- and 66-kDa subunits comprising equine infectious anemia virus reverse transcriptase (EIAV RT) is repo rted. Both polypeptides sedimented as stable homodimers (molecular mas s, 102 and 132 kDa, respectively) when analyzed by rate sedimentation through glycerol gradients. Consistent with their dimer composition, e ach preparation displayed considerable levels of both RNA and DNA-depe ndent DNA polymerase activity on different homopolymeric template/prim er combinations. However, a detailed analysis of the polymerization pr oducts indicated qualitative differences. Whereas p66 EIAV RT proceede d essentially unimpaired along both RNA and DNA templates, p51-catalyz ed DNA synthesis was interrupted close to or in the immediate vicinity of the primer. A series of ''programed'' 2-step polymerization reacti ons suggests that p51 EIAV RT enters an abortive mode of polymerizatio n. Duplication of this observation with p51 human immunodeficiency vir us-1 RT, together with recent observations from murine RT, suggests th at lack of a ribonuclease H domain and loss of contact with the nascen t product from the polymerase active center have profound consequences on the mode of polymerization.