The application of integration profiles to identify novel genes that contribute to heterochromatin in fission yeast

Authors

• SY Lee
• Steve Hung
• Kory Johnson
• Henry Levin

Abstract

Heterochromatin is a repressive chromatin state that is characterized by densely packed nucleosome and low transcriptional activity. Besides repressing transcription, heterochromatin performs many diverse functions. Because of its advantages for studying heterochromatic function, S. pombe is a valuable model system for investigating heterochromatin mechanisms. Identification of heterochromatin factors has not been exhaustive, and it is therefore likely that additional factors remain to be discovered. Previously, we developed a transposon-based approach called integration profiling that saturates the genome with insertions and measures the contribution of each ORF in S. pombe. We have now applied this novel technology to identify new genes important for heterochromatin. These integration profiles include 1 million sites and identified a total of 179 candidate genes that may contribute to heterochromatin. This gene set was significantly enriched for factors with known heterochromatic functions, such as chromatin silencing and regulation of histone methylation. Interestingly, the candidate set included 57 essential genes and these were enriched for proteins associated with mRNA cleavage and (or) polyadenylation of mRNA. Guided by the integration profile we created a C-terminal truncation of Iss1, a factor involved in polyadenylation and cleavage. This mutant showed reduced gene silencing in pericentromeric heterochromatin, indicating this gene is important for heterochromatin. Assays that measure H3K9me indicated that Iss1 mediates heterochromatin formation in parallel with RNAi. Because many of our candidates were not previously known to contribute to heterochromatin, we believe that our studies will provide new insights into the mechanism of heterochromatin.

Scientific Focus Area: Chromosome Biology

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