Histone sumoylation is associated with transcriptional repression.

Histone proteins are subject to modifications, such as acetylation, methylation, phosphorylation, ubiquitination, glycosylation, and ADP ribosylation, some of which are known to play important roles in the regulation of chromatin structure and function. Here we report that histone H4 is modified by small ubiquitin-related modifier (SUMO) family proteins both in vivo and in vitro. H4 binds to the SUMO-conjugating enzyme (E2), UBC9, and can be sumoylated in an E1 (SUMO-activating enzyme)- and E2-dependent manner. We present evidence suggesting that histone sumoylation mediates gene silencing through recruitment of histone deacetylase and heterochromatin protein 1.