sentence: Mutations in Saccharomyces cerevisiae SPT6 cause genome-wide changes in histone occupancy ( 13 – 16 ) and impair several histone modifications , including H3K36 di - and tri-methylation ( H3K36me2 / me3 ) catalyzed by the H3K36 methyltransferase Set2 ( 17 – 20 ) .