The evolutionarily conserved factor Sus1/ENY2 plays a role in telomere length maintenance

Sus1 is a conserved protein involved in histone H2B de-ubiquitination and mRNA export from the nucleus in eukaryotes. Previous studies implicated Sus1 partners in genome integrity including telomere homeostasis. However, the implication of Sus1 in telomere maintenance remains largely unknown. In this study, we found that yeast Sus1 interacts physically and genetically with factors involved in telomere maintenance and its absence leads to elongated telomeres. Deletion of several of Sus1’s partners also leads to longer telomeres. Our results rule out a direct role for Sus1 in recruiting telomerase subunits to telomeres. However, we observe that deletion of SUS1 leads to elongated telomeres even in the presence of mutations like sem1 Δ, esc2 Δ and rsc2 Δ, which cause telomere shortening. We find that rsc2 Δ (short telomeres) have reduced levels of mono-ubiquitinated histone H2B at lysine 123 (H2BK123ub 1 ), whereas sus1 Δ mutants or double-mutants sus1 Δ rsc2 Δ exhibit longer telomeres and higher H2BK123ub 1 levels. These results suggest that Sus1 activity as a H2B de-ubiquitination modulator plays a role in negatively regulating telomere length. Our results provide solid evidence for a role of Sus1 in negatively regulating telomere length through the modulation of H2BK123 mono-ubiquitination and its interaction with the nuclear pore complex.