Reverse transcriptases can clamp together nucleic acids strands with two complementary bases at their 3'-termini for initiating DNA synthesis.
We present evidence that the reverse transcriptase (RT) of human immunodeficiency virus type-1 stabilizes in vitro very short (2-nt) duplexes of 3'-overhangs of the primer strand that are annealed to complementary dinucleotides tails of DNA or RNA template strands, provided that these sequences contain at least one C or G. This RT-induced strand 'clamping' activity promotes RT-directed DNA synthesis. This function is achieved only when the functional template strand is adjacent to a second DNA or RNA segment, annealed upstream to most of the primer (without gaps). The combined clamp/polymerase activity is typical to RTs, as it was found in different RTs from diverse retroviral groups, whereas cellular DNA-polymerases (devoid of 3'→5' exonucleolytic activity) showed no clamp activity. The clamp-associated DNA-binding activity is markedly stabilized by dGTP, even when dGTP is not incorporated into the nascent DNA strand. The hereby-described function can help RTs in bridging over nicks in the copied RNA or DNA templates, encountered during reverse transcription. Moreover, the template-independent blunt-end synthesis of RTs can allow strand transfers onto compatible acceptor strands while synthesizing DNA. These RT properties can shed light on potentially-new roles of RTs in the reverse-transcription process and define new targets for anti-retroviral drugs.
Oz-Gleenberg
Iris
I
Department of Cell and Developmental Biology, Sackler School of Medicine,Tel Aviv University, Tel Aviv, 69978, Israel.
Herschhorn
Alon
A
Hizi
Amnon
A
D001483:Base Sequence; D004247:DNA / Q000096:biosynthesis* / Q000737:chemistry; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D054303:HIV Reverse Transcriptase / Q000378:metabolism*; D012313:RNA / Q000737:chemistry; D013698:Templates, Genetic
D012313:RNA; D004247:DNA; C514824:reverse transcriptase, Human immunodeficiency virus 1; D054303:HIV Reverse Transcriptase; D004259:DNA-Directed DNA Polymerase