Ty1 retrovirus-like element Gag contains overlapping restriction factor and nucleic acid chaperone functions |
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| Authors: | Yuri Nishida Katarzyna Pachulska-Wieczorek Leszek B?aszczyk Agniva Saha Julita Gumna David J. Garfinkel Katarzyna J. Purzycka |
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| Affiliation: | 1Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, USA;2Department of Structural Chemistry and Biology of Nucleic Acids, Institute of Bioorganic Chemistry, Polish Academy of Sciences, 61-704 Poznan, Poland;3Institute of Computing Science, Poznan University of Technology, 60-965 Poznan, Poland |
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| Abstract: | Ty1 Gag comprises the capsid of virus-like particles and provides nucleic acid chaperone (NAC) functions during retrotransposition in budding yeast. A subgenomic Ty1 mRNA encodes a truncated Gag protein (p22) that is cleaved by Ty1 protease to form p18. p22/p18 strongly inhibits transposition and can be considered an element-encoded restriction factor. Here, we show that only p22 and its short derivatives restrict Ty1 mobility whereas other regions of GAG inhibit mobility weakly if at all. Mutational analyses suggest that p22/p18 is synthesized from either of two closely spaced AUG codons. Interestingly, AUG1p18 and AUG2p18 proteins display different properties, even though both contain a region crucial for RNA binding and NAC activity. AUG1p18 shows highly reduced NAC activity but specific binding to Ty1 RNA, whereas AUG2p18 shows the converse behavior. p22/p18 affects RNA encapsidation and a mutant derivative defective for RNA binding inhibits the RNA chaperone activity of the C-terminal region (CTR) of Gag-p45. Moreover, affinity pulldowns show that p18 and the CTR interact. These results support the idea that one aspect of Ty1 restriction involves inhibition of Gag-p45 NAC functions by p22/p18-Gag interactions. |
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