Bis-(2P P-deoxynucleoside) 5P P,5P P-tetraphosphates and bis-(2P P-deoxynucleoside) 5P P,5P P-triphosphates were shown to be a new type of substrate for several DNA polymerases of human, bacterial and viral origin. Their substrate properties depend both on their structure and on the nature of the enzyme. They are incorporated by both termini in correspondence with the template nucleotide program in the active center. The results obtained support the mechanism of their direct incorporation rather than prior hydrolysis to dNTP. The highest activity of these compounds was observed for HIV reverse transcriptase. The probable biological significance of the reaction is discussed.z 1999 Federation of European Biochemical Societies.

Stavudine administration did not increase the frequency of Y181I/C reverse transcriptase (RT) mutations in non-nucleoside reverse transcriptase inhibitor (NNRTI)-treated patients. However, recombinant Y181C HIV-1 showed reduced stavudine susceptibility with respect to both recombinant wild-type and K103N HIV-1 strains. In addition, recombinant Y181I RT enzyme showed reduced susceptibility to stavudine with respect to both wild-type and K103N RT. A previously unnoticed role of Y181I/C RT changes selected by nevirapine or other NNRTI in determining stavudine resistance is documented.

Recombinant HIV-1 reverse transcriptase (RT) carrying non-nucleoside inhibitors (NNRTIs) resistance mutation at codon 181 showed reduced incorporation and high efficiency of phosphorolytic removal of stavudine, a nucleoside RT inhibitor. These results reveal a new mechanism for cross-resistance between different classes of HIV-1 RT inhibitors.

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