Characterization of human T-cell leukemia virus type I integrase expressedin Escherichia coli

The C-terminal part of the pol gene of the human T-cell leukemia virus type I (HTLV-I) is predicted to encode the integrase (IN) of the virus; however , this protein has not yet been detected in virions or infected cells. We e xpressed the putative IN from an infectious molecular clone of HTLV-I in Es cherichia coli. Comparison with protein resulting from coexpression of HTLV -I protease (PR) and Pol in insect cells indicated that the bacterially exp ressed protein is identical with or very similar to IN released from a PR-P ol precursor by proteolytic cleavage. HTLV-I IN was purified from E. coli u nder native conditions. The protein behaved like a dimer in size-exclusion chromatography. It carried out activities characteristic of retroviral IN w ith high efficiency, displaying a strong preference for US-derived vs. U3-d erived sequences in the processing and strand-transfer reactions. In the di sintegration reaction, HTLV-I IN not only accepted the double-stranded bran ched substrate corresponding to the product of a strand-transfer reaction, but was also able to carry out a phosphoryl transfer on a branched molecule with a single-stranded or a single adenosine overhang.