![]() Replication involves reverse transcription of the RNA genome within ribonucleoprotein complexes, transport of the cDNA copy to the nucleus, integration of the cDNA into the host genome, transcription of the integrated provirus or element and transport of one or more RNA species to the cytoplasm for translation and packaging into viral or viral-like particles. Retroviruses and retroviral-like transposable elements have compact genomes, yet their replication is a complex, multiphasic process. These findings uncover a role for the Ty1 promoter in integrating signals from diverse host factors to modulate Ty1 RNA biogenesis or fate. Many U3DRs had minimal effects on levels of Ty1 RNA, Ty1i RNA or p22-Gag. 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. Thirty-one U3DRs failed to modulate P PSP2-Ty1 his3AI retromobility, suggesting dependence on the architecture of U3. Nineteen U3-dependent regulators (U3DRs) also controlled retromobility of Ty1 his3AI driven by the weak, TATA-less PSP2 promoter, suggesting reliance on the low activity of U3. The second class of 51 genes regulated retromobility of Ty1 his3AI driven only from the U3 promoter. The first class comprising 82 genes that regulated Ty1 his3AI retromobility independently of U3 is enriched for RHF genes that restrict the G1 phase of the cell cycle and those involved in transcriptional elongation and mRNA catabolism. Two classes of genes, each including both RHFs and RTTs, were identified. To characterize the U3-dependence of other Ty1 regulators, we screened a library of 188 known rhf and rtt mutants for altered retromobility of Ty1 his3AI expressed from the strong, TATA-less TEF1 promoter or the weak, TATA-containing U3 promoter. Well-characterized examples include MED3 and MED15, 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. Several hundred RHF and RTT genes encoding co-factors and restrictors of Ty1 retromobility, respectively, have been identified. The Ty1 retrotransposon family is maintained in a functional but dormant state by its host, Saccharomyces cerevisiae. 2Department of Biomedical Sciences, School of Public Health, University at Albany, Albany, NY, United States.1Laboratory of Molecular Genetics, Wadsworth Center, New York State Department of Health, Albany, NY, United States.
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