Host genes that affect the target-site distribution of the yeast retrotransposon Tyl

We report here a simple genetic system for investigating factors affecting Ty1 target-site preference within an RNAP II transcribed gene. The target i n this system is a functional fusion of the regulatable MET3 promoter with the URA3 gene. We found that the simultaneous inactivation of Hir3 (a histo ne transcription regulator) and Cac3 (a subunit of the chromatin assembly f actor I), which was previously shown by us to increase the Ty1 transpositio n rate, eliminated the normally observed bias for Ty1 elements to insert in to the 5' vs. 3' regions of the MET3-URA3 and CAN1 genes. The double cad hi r3 mutation also caused the production of a short transcript from the MET3- URA3 fusion under both repressed and derepressed conditions. In a hir3 Delt a single-mutant strain, the Ty1 target-site distribution into MET3-URA3 was altered only when transposition occurred while the MET3-URA3 fusion was ac tively transcribed. In contrast, transcription of the MET3-URA3 fusion did not alter the Ty1 target-site distribution in wild-type or other mutant str ains. Deletion of RAD6 was shown to alter the Ty1 target-site preference in the MET3-URA3 fusion and the LYS2 gene. These data, together with previous studies of Ty1 integration positions at CAN1 and SUP4, indicate that the r ad6 effect on Ty1 target-site selection is not gene specific.