DNA Synthesis by HIV-1 Reverse Transcriptase at the Central Termination Site

Human immunodeficiency virus, type 1 (HIV-1) reverse transcriptase (RT) terminates plus-strand DNA synthesis at the center of the HIV-1 genome, a process important for HIV-1 infectivity. The central termination sequence contains two termination sites (Ter1 and Ter2) located at the 3'-end of A(n)T(m) motifs, and the narrowing of the DNA minor groove generated by these motifs is responsible for termination. Kinetic data associated with the binding of RT and its ability to elongate in vitro various DNA duplexes and triplexes surrounding the Ter2 terminator were analyzed using a simple kinetic scheme. At Ter2, RT still displays a reasonable affinity for the corresponding DNA, but the binding of the next nucleotide and above all its incorporation rate are markedly hampered. Features affecting the width of the minor groove act directly at this last step. The constraint exerted against elongation by the A(n)T(m) tract persists at two positions downstream of the terminator.