Reverse transcriptase associated with avian sarcoma-leukosis viruses. II. Comparison of subunit structure and...

The three enzyme forms (alpha, alpha beta-, and beta-form) of the RNA-dependent DNA polymerase (the reverse transcriptase) from three strains of avian sarcoma virus (ASV B77, ASV tsLA334, and ASV QV2) and one exogenous (avian myeloblastosis virus (AMV)) and one endogenous avian leukosis virus (Rous-associated virus type-0 (RAV-0) were compared with each other in subunit structure and catalytic properties. Despite the gross similarity in the subunit molecular weight (Mr(alpha) = 65,000 and Mr(beta) = 92,000), minor differences were found in the molecular size of the subunit as determined by SDS-gel electrophoresis, the order being ASV tsLA334 less than or equal to ASV QV2 less than ASV B77 less than or equal to RAV-0 = AMV. The structural differences were supported by analysis of peptide fragments after treatment with S. aureus V8 protease. Although the general catalytic properties of the purified enzymes from the five virus strains were similar, the selectivety of template-primer differed in the RAV-0 enzymes. The template-primer selectivity of the reverse transcriptases from all five virus strains tested was also found to be greatly influenced by the reaction temperature for DNA synthesis, resulting in a temperature-dependent increase of poly(dG) synthesis over [(A)m] . [(dT)12-18]-dependent poly(dT) synthesis. The RAV-0 enzymes required a lower temperature for DNA synthesis, particularly for [(C)n] . [(dG)12-18]-dependent poly(dG) synthesis.