DNA CURVATURE CONTROLS TERMINATION OF PLUS STRAND DNA-SYNTHESIS AT THE CENTER OF HIV-1 GENOME

In vivo and in vitro, reverse transcriptase (RT) from human immunodefi ciency virus type 1 (HIV-1) terminates plus strand synthesis at the ce ntre of the viral genome. The central termination sequence (CTS) conta ins curved DNA fragments located upstream of each terminator site. Two different models, relying either on the A-tract or general sequence r oll assumptions, were used to predict the extent and the direction of this curvature as well as to design mutants, which abolished it. Strai ghtening of each curved element abolished termination at the site loca ted immediately downstream from the curvature. When synthesis was perf ormed on the other strand and in the opposite direction, the two curve d elements C1 and C2 associated with the two termination sites Ter1 an d Ter2, led again to termination of DNA synthesis. Therefore, terminat ion occurred as a nascent bent duplex was synthesized within the templ ate primer binding cleft of RT, even when putative strand-specific mot ifs have been removed by the inversion. Computation of DNA paths upstr eam of other known arrest sites suggested that this feature was of gen eral relevance for termination. At the CTS, termination occurred more precisely at the 3' end of an A(n)T(m) motif (n + m = 7). The possible structures, adopted by this motif, are discussed and confronted with the present crystallographic and biochemical data obtained on HIV-1 RT -DNA interactions and on HIV-1 RT processivity. (C) 1997 Academic Pres s Limited.