Recognition of methylated histones: new twists and variations.

Histone tails undergo methylation at their lysines and arginines. These chemical marks act as traffic signals that direct activity of chromatin remodeling complexes to appropriate regions of the genome. A surprisingly diverse group of effector protein modules in chromatin remodeling complexes and their associated factors are involved in the recognition of histone methyllysines. Previous studies generally painted a picture of individual lysines recognized by these protein modules in a 1:1 fashion. However, recent structural studies show more complex interactions where the critical lysines are recognized in pairs, or in the context of nucleosomal DNA, or within the central pore of repeat motifs. These interactions extend our understanding of how histone tail recognition can be enhanced through coupled interactions within a single module or through the cooperation of two different molecules.