The various modifications showed distinctive "personalities," each preferentially associating with particular regulatory regions of genes.
Looking for Patterns
Mapping many modifications enabled the researchers to explore whether different types tend to appear together in the same type of DNA regulatory regions. They found that some recurring combinations did occur frequently at "promoter" and "enhancer" regions in DNA, which are known to increase the activity of nearby genes. In particular, the team identified one combination of 17 modifications that was present in more than a quarter of the more than 12,000 promoter regions they examined.
On average, the genes corresponding to this "backbone" set were expressed more actively. That is to say, they were activated, setting the cellular machinery in motion to produce specific proteins, the workhorses of most life processes.
The rich relationships detected by the researchers among the various histone modifications suggests that specific combinations might carry specific meanings. Previous researchers have proposed a "histone code" hypothesis, which posits that a particular combination of modifications may be recognized by a particular protein module. Some scientists believe such histone code may determine the activity of a given gene.
But, cautions Dr. Zhang, while there are patterns, like the backbone, that are highly correlated, "none of them has exact predictive value." He maintains "there must be something else" that also affects
|Contact: Jim Bono|
Cold Spring Harbor Laboratory