SWRred not shaken; mixing the histones.

The recently isolated SWR1 complex catalyzes an ATP-dependent histone exchange with specificity for the histone variant H2A.Z. This provides a new theme in chromatin remodeling mechanisms and an explanation of how histone variants are incorporated into the nucleosome outside of S phase. In connection with the isolation of histone variant specific chaperone complexes, we are beginning to see the mechanisms that mix the histone octamer with intriguing implications for epigenetic inheritance.