Recent findings suggest important roles for nuclear organization in gene expression. In contrast, little is known about how nuclear organization contributes to genome stability. Epistasis analysis (E-MAP) using DNA repair factors in yeast indicated a functional relationship between a nuclear pore subcomplex and Slx5/Slx8, a small ubiquitin-like modifier (SUMO)–dependent ubiquitin ligase, which we show physically interact. Real-time imaging and chromatin immunoprecipitation confirmed stable recruitment of damaged DNA to nuclear pores. Relocation required the Nup84 complex and Mec1/Tel1 kinases. Spontaneous gene conversion can be enhanced in a Slx8- and Nup84-dependent manner by tethering donor sites at the nuclear periphery. This suggests that strand breaks are shunted to nuclear pores for a repair pathway controlled by a conserved SUMO-dependent E3 ligase.

Chromatin in the interphase nucleus moves in a constrained random walk. Despite extensive study, the molecular causes of such movement and its impact on DNA-based reactions are unclear. Using high-precision live fluorescence microscopy in budding yeast, we quantified the movement of tagged chromosomal loci to which transcriptional activators or nucleosome remodeling complexes were targeted. We found that local binding of the transcriptional activator VP16, but not of the Gal4 acidic domain, enhances chromatin mobility. The increase in movement did not correlate strictly with RNA polymerase II (PolII) elongation, but could be phenocopied by targeting the INO80 remodeler to the locus. Enhanced chromatin mobility required Ino80's ATPase activity. Consistently, the INO80-dependent remodeling of nucleosomes upon transcriptional activation of the endogenous PHO5 promoter enhanced chromatin movement locally. Finally, increased mobility at a double-strand break was also shown to depend in part on the INO80 complex. This correlated with increased rates of spontaneous gene conversion. We propose that local chromatin remodeling and nucleosome eviction increase large-scale chromatin movements by enhancing the flexibility of the chromatin fiber.[Keywords: chromatin remodeling; nuclear organization; transcription; VP16; Ino80; fluorescence microscopy; homologous recombination] Supplemental material is available for this article.Received August 15, 2011; revised version accepted January 13, 2012.DNA-based transactions such as transcription, replication, and repair take place in distinct nuclear subcompartments. Transcriptional silencing is frequently associated with the nuclear envelope or occurs near nucleoli (Towbin et al. 2009), whereas the activation of tissue-specific genes correlates with a shift of the relevant genes away from the nuclear periphery (Egecioglu and Brickner 2011). In contrast, genes activated under conditions of nutrient or temperature stress move to nuclear pores when they are induced (Taddei 2007). Finally, some types of damagenamely, irreparable DNA double-strand breaks (DSBs), collapsed replication forks, and eroded telomeres-relocate to nuclear pores to be processed for repair, unlike DSBs that can be repaired by recombination with a homologous template (for review, see Nagai et al. 2010). For these relocalization events to occur, whether at a promoter, a replication fork, or a DSB, chromatin must be mobile.Rapid time-lapse fluorescence microscopy of GFP-LacItagged genomic loci has shown that individual chromosomal domains move constantly in a near-random walk within a restrained volume of the nucleus (Hubner and Spector 2010). The measured radius of constraint for the movement of an average chromosomal locus (;0.6 mm) was roughly similar in every species investigated, although mobility was also shown to be influenced by local chromatin context (Marshall et al. 1997;Heun et al. 2001;Vazquez et al. 2001;Chubb et al. 2002;Gartenberg et al. 2004). For instance, lacO arrays inserted near budding yeast ce...