Mapping the multimerization domains of the Gag protein of yeast retrotransposon Ty1

The two-hybrid system was used to define regions of the Ty1 Gag protein responsible for multimerization. Gag truncations lacking the first 146 or the last 97 amino acids (Gag is 440 amino acids in length) interact. A severely C-terminally truncated molecule (lacking the last 207 amino acids) was the smallest truncation to interact, suggesting that some protein-protein interactions between Gag molecules are mediated through the first 233 amino acids. However, an internal deletion of amino acids 147 to 233 does not abolish Gag-Gag interaction, indicating that more than one region can mediate Gag interaction. Surprisingly, we found that a truncation lacking the last 97 amino acids interacts with itself but not with full-length Gag. This is apparently due to an artifact of the two-hybrid assay, since these same molecules coassemble with wild-type Gag into Ty1 virus-like particles.