H2A.Z-Mediated Genome-Wide Chromatin Specialization

The characterization of the involvement of different histone post-translational modifications (PTMs) and histone variants in chromatin structure has represented one of the most recurrent topics in molecular biology during the last decade (since 1996). The interest in this topic underscores the critical roles played by chromatin in such important processes as DNA packaging, DNA repair and recombination, and regulation of gene expression. The genomic information currently available has pushed the boundaries of this research a step further, from the study of local domains to the genome- wide characterization of the mechanisms governing chromatin dynamics. How the heterchromatin and euchromatin compartmentalization is established has been the subject of recent extensive research. Many PTMs, as well as histone variants have been identified to play a role, including the replacement of histone H2A by the histone variant H2A.Z. Several studies have provided support to a role for H2A.Z (known as Htz1 in yeast) in transcriptional regulation, chromosome structure, DNA repair and heterochromatin formation. Although the mechanisms by which H2A.Z defines different structural regions in the chromatin have long remained elusive, various reports published last year have shed new insight into this process. The present mini review focuses its attention on the genome-wide distribution of H2A.Z, with special attention to the mechanisms involved in its distribution and exchange as well as on the role of its N-terminal acetylation.