Function
Integrase catalyzes viral DNA integration into the host chromosome, by performing a series of DNA cutting and joining reactions. This enzyme activity takes place after virion entry into a cell and reverse transcription of the RNA genome in dsDNA. The first step in the integration process is 3' processing. This step requires a complex comprising at least the viral genome, matrix protein, and integrase. This complex is called the pre-integration complex (PIC). The integrase protein removes 2 nucleotides from the 3' end of the viral DNA right (U5) end, leaving the left (U3) intact. In the second step, the PIC enters cell nucleus. This process is mediated through the integrase and allows the virus to infect both dividing (nuclear membrane disassembled) and G1/S-arrested cells (active translocation), but with no viral gene expression in the latter. In the third step, termed strand transfer, the integrase protein joins the previously processed 3' ends to the 5' ends of strands of target cellular DNA at the site of integration. It is however not clear how integration then proceeds to resolve the asymmetrical cleavage of viral DNA (By similarity).
Sequence
MDLLKPLTVERKGVKIKGYWDSQADITCVPKDLLQGEEPVRQQNVTTIHGTQEGDVYYVNLKIDGRRINTEVIGTTLDYAIITPGDVPWILKKPLELTIKLDLEEQQGTLLNNSILSKKGKEELKQLFEKYSALWQSWENQVGHRRIRPHKIATGTVKPTPQKQYHINPKAKPDIQIVINDLLKQGVLIQKESTMNTPVYPVPKPNGRWRMVLDYRAVNKVTPLIAVQNQHSYGILGSLFKGRYKTTIDLSNGFWAHPIVPEDYWITAFTWQGKQYCWTVLPQGFLNSPGLFTGDVVDLLQGIPNVEVYVDDVYISHDSEKEHLEYLDILFNRLKEAGYIISLKKSNIANSIVDFLGFQITNEGRGLTDTFKEKLENITAPTTLKQLQSILGLLNFARNFIPDFTELIAPLYALIPKSTKNYVPWQIEHSTTLETLITKLNGAEYLQGRKGDKTLIMKVNASYTTGYIRYYNEGEKKPISYVSIVFSKTELKFTELEKLLTTVHKGLLKALDLSMGQNIHVYSPIVSMQNIQKTPQTAKKALASRWLSWLSYLEDPRIRFFYDPQMPALKDLPAVDTGKDNKKHPSNFQHIFYTDGSAITSPTKEGHLNAGMGIVYFINKDGNLQKQQEWSISLGNHTAQFAEIAAFEFALKKCLPLGGNILVVTDSNYVAKAYNEELDVWASNGFVNNRKKPLKHISKWKSVADLKRLRPDVVVTHEPGHQKLDSSPHAYGNNLADQLATQASFKVHMTKNPKLDIEQIKAIQACQNNERLPVGYPKQYTYELQNNKCMVLRKDGWREIPPSRERYKLIKEAHNISHAGREAVLLKIQENYWWPKMKKDISSFLSTCNVCKMVNPLNLKPISPQAIVHPTKPFDKFYMDYIGPLPPSEGYVHVLVVVDAATGFTWLYPTKAQTSKATIKVLNHLTGLAIPKVLHSDQGSAFTSEEFAQWAKERNIQLEFSTPYHPQSSGKVERKNSEIKKLLTKLLVGRPLKWYNLISSVQLALNNTHVVSTKYTPHQLMFGIDCNLPFANKDTLDWTREEELALLQEIRESLQHPVQPPTCSGWSPYVGQLVQERVYRPSQLRPKWRKPTKVLEILNPRTVIIVDHLGQRKSVSIDNLKPTAHQHNGTRTCDDPEGMDGMECSQTTTETSVDSS