Tetramer model trashed

Two models of histone incorporation

ﾩ 2004 ELSEVIER

The paper:

The finding:

Yoshihiro Nakatani's group at Dana Farber Cancer Institute and Genevi￨ve Almouzni's group at Curie Institute in France identified the chaperones responsible for depositing histone complexes H3.1 and H3.3 into chromatin through two distinct pathways. Steven Henikoff at Fred Hutchinson Cancer Research Center says, "It was very satisfying to see their results," because he had suspected that two pathways exist - replication-independent and replication-dependent - and Nakatani's biochemistry confirmed it.

The surprise:

During purification of the histone complexes the authors found evidence that the complexes possessed a pair of H3/H4 histone dimers, rather than the tetramer that had been hypothesized. Nakatani says a dimer model of the histone complex helps explain how the histone complex segregates equally during DNA replication.

The follow-up:

Nakatani has since found further evidence of the histone dimer in complexes purified from the cytoplasm. He says he's recently found that the histone chaperone ASF1 blocks formation of a tetramer by binding to the domain where the H3 histones of each H3/H4 dimer interact to form a tetramer.

Nakatani's advice:

Although many use the histone tetramer as a substrate during chaperone studies, Nakatani says, "Everybody should use the dimer form for a substrate, because that is what is found in vivo."