Multimerization determinants reside in both the catalytic core and C terminus of avian sarcoma virus integrase

We have shown previously that the active form of avian sarcoma virus integrase (ASV IN) is a multimer. In this report we investigate IN multimerization properties by a variety of methods that include size exclusion chromatography, chemical cross-linking, and protein overlay assays. We show that removal of the nonconserved C-terminal region of IN results in a reduced capacity for multimerization, whereas deletion of the first 38 amino acids has little effect on the oligomeric state. Binding of a full-length IN fusion protein to various IN fragments indicates that sequences in both the catalytic core (residues 50-207) and a C-terminal region (residues 201-240) contribute to IN self-association. We also observe that the isolated C-terminal fragment (residues 201-286) is capable of self-association. Finally, a single amino acid substitution in the core domain (S85G) produces a severe defect in multimerization. We conclude from these analyses that both the catalytic core and a region in the nonconserved C terminus are involved in ASV integrase multimerization. These results enhance our understanding of intergrase self-association determinants and define a major role of the C-terminal region of ASV integrase in this process.