Cohesin‐dependent association of tRNA genes with nuclear pore complexes in budding yeast

Abstract

Budding yeast tRNA genes, tDNAs, are located throughout the genome yet large families of the genes cluster together at the nucleolus. Formation of the tDNA clusters is condensin‐dependent while their nucleolar localization is microtubule‐dependent (Haeusler et al., Genes & Development, 2008). Previously we found that tT(AGU)C, the tDNA that creates a boundary at the heterochromatic HMR locus, situates infrequently at the nucleolus (Valenzuela et al., Molecular and Cellular Biology, 2008). Using fluorescence microscopy, we show that tT(AGU)C colocalizes with nuclear pore complexes (NPCs) and that this association occurs primarily in M phase of the cell cycle. Building on recent mapping of nucleoporins to tT(AGU)C (Ruben et al., PLoS ONE, 2011), we show by chromatin immunoprecipitation that Nup60 is enriched at tT(AGU)C and other tDNAs in M phase. Association of these loci with NPCs requires tDNA gene sequences, Nup60 and cohesin. DNA circles bearing tT(AGU)C also colocalize with NPCs, indicating that the association requires only the tDNA and not other more global features of chromosome structure. Taken together, these results reveal an unexpected yet general phenomenon of cohesin‐dependent tDNA‐NPC association at M phase. Finally, using RT‐qPCR we find that the NPC‐tDNA association correlates with an increase in nascent tRNA levels at M phase. We speculate that the NPC‐tDNA association facilitates cell‐cycle dependent expression of tDNAs. This research was supported by grants from NIH (GM51402).