Ten-kilodalton domain in Ty3 Gag3-Pol3p between PR and RT is dispensable for 53 transposition

Ty3 is a gypsy-type, retrovirus-like element found in the budding yeast Sac charomyces cerevisiae. In cells overexpressing Ty3 under the GAL1 upstream activation sequence, Ty3 RNA, proteins, and DNA are made. Elucidation of th e molecular masses and amino-terminal sequences of protease and reverse tra nscriptase indicated the existence of an additional intervening domain, des ignated J, in the Ty3 Gag3-Pol3p polyprotein. A region analogous to J can b e found in many retrotransposable elements closely related to Ty3; however, J does not correspond to any of the highly conserved retroviral protein do mains. Ty3 mutants deleted for the J-coding region showed moderately reduce d transposition frequency but greatly reduced levels of Ty3 DNA. These resu lts show that under galactose regulation, the Ty3 J domain is not absolutel y essential.