Reliance of Host-Encoded Regulators of Retromobility on Ty1 Promoter Activity or Architecture.

The Ty1 retrotransposon family is maintained in a functional but dormant state by its host, . Several hundred and genes encoding co-factors and restrictors of Ty1 retromobility, respectively, have been identified. Well-characterized examples include and , encoding subunits of the Mediator transcriptional co-activator complex; control of retromobility by Med3 and Med15 requires the Ty1 promoter in the U3 region of the long terminal repeat. To characterize the U3-dependence of other Ty1 regulators, we screened a library of 188 known and mutants for altered retromobility of Ty1 expressed from the strong, TATA-less promoter or the weak, TATA-containing U3 promoter. Two classes of genes, each including both s and s, were identified. The first class comprising 82 genes that regulated Ty1 retromobility independently of U3 is enriched for genes that restrict the G1 phase of the cell cycle and those involved in transcriptional elongation and mRNA catabolism. The second class of 51 genes regulated retromobility of Ty1 driven only from the U3 promoter. Nineteen U3-dependent regulators (U3DRs) also controlled retromobility of Ty1 driven by the weak, TATA-less promoter, suggesting reliance on the low activity of U3. Thirty-one U3DRs failed to modulate P -Ty1 retromobility, suggesting dependence on the architecture of U3. To further investigate the U3-dependency of Ty1 regulators, we developed a novel fluorescence-based assay to monitor expression of p22-Gag, a restriction factor expressed from the internal Ty1i promoter. Many U3DRs had minimal effects on levels of Ty1 RNA, Ty1i RNA or p22-Gag. These findings uncover a role for the Ty1 promoter in integrating signals from diverse host factors to modulate Ty1 RNA biogenesis or fate.