Mutational analysis of the N-terminus of Moloney murine leukemia virus integrase

The retroviral integrase (IN) carries out the integration of viral DNA into the host genome. The IN protein consists of three domains: the N-terminal HHCC motif, the catalytic core region, and the C-terminus. The Moloney murine leukemia virus (M-MuLV) IN encodes a unique 45-amino-acid domain N-terminal to the HHCC motif. The function of the N-terminus of M-MuLV IN was studied through deletional and mutational analyses. The IN 1-105 domain was dissected into two halves expressing either the unique N-terminus or the HHCC domain. Although the parental IN 1-105 could functionally complement the core-C-terminus for integration reactions, neither half of the N-terminus was sufficient. Partial complementation of strand transfer, but not 3prime prime or minute processing, could be obtained through mixing the two halves. The dimerization of the M-MuLV N-terminus was dependent on the expression of the intact 1-105. Critical basic amino acids within the HHCC domain which are required for 3' processing and strand transfer reactions were identified through alanine mutagenesis. Loss of in vitro strand transfer activity correlated with loss of viral titer in vivo for this cluster of basic amino acids within the HHCC domain.