"In our experiments, we saw SUMO binding to histones across the genome, suggesting that if this mechanism went wrong, it could have a dramatic effect," says Berger. "We know, for example, that histones are important in a number of cancers, and SUMO may be a significant part of that."
The research team also noted a dynamic interplay between the addition of a SUMO protein to a histone ?sumoylation ?and the addition of either an acetyl group or a ubiquitin protein to a histone. The processes appear to be mutually exclusive.
"Acetylation and ubiquitylation have both been shown in earlier studies to activate gene expression," says Kristin Ingvarsdottir, co-lead author on the Genes & Development study. "Sumoylation, on the other hand, is involved in gene repression, so it makes sense that it might exist in an either/or relationship with acetylation or ubiquitylation."
Another observation made during the study was that slightly higher levels of sumoylation occur near the tips of the chromosomes, the telomeres, which are known to play a central role in maintaining genomic stability. Instability in the telomeres has been linked to aging in humans and an elevated risk for aging-related diseases, the most prominent of which is cancer.