EFFECT OF A THIOBENZIMIDAZOLONE DERIVATIVE ON DNA STRAND TRANSFER CATALYZED BY HIV-1 REVERSE-TRANSCRIPTASE

Thiobenzimidazolone (TIBO) derivatives are known inhibitors of the DNA polymerase activity of human immunodeficiency virus type 1 (HIV-1) re verse transcriptase (RT). The effect of a TIBO derivative yl)-imidazol [4,5,1-jk]1,4-benzodiazapine-2-thione) DNA strand transfer reaction ca talyzed by HIV-1 RT (which is a function of both the DNA polymerase an d RNase H activities) was investigated by delineating the effect of th e drug on the constitutive DNA polymerase and RNase H activities. Sing le nucleotide incorporation on template-primer 1 was used to study the DNA polymerase activity of HIV-1 RT while template-primer 2 was used to study the effect of TIBO on the RNase H activity (polymerase indepe ndent). The drug was found to decrease the amplitude of the presteady- state burst when preequilibrated with the enzyme substrate complex bes ides decreasing the steady-state rate of single nucleotide incorporati ons. In the absence of preincubation, TIBO did not affect the burst am plitude but decreased the steady-state rate after the pre-transient ph ase. This suggested that binding of TIBO to RT was affected by the pre sence of template-primer and required dissociation of the enzyme from the template primer for effective binding. The polymerase-independent RNase H activity was activated in the presence of TIBO. The effect of TIBO on the overall process of DNA strand transfer is a balance betwee n its inhibition of the polymerase activity and its activation of the RNase H activity.