Heterochromatin condensation, shown by histone H3 phosphorylation (black, above dotted line), is disrupted in cells lacking Myb (below).

LIPSICK/MACMILLAN

Gene-rich euchromatin and largely untranscribed heterochromatin may follow different rules to prepare for mitosis, according to J. Robert Manak, Joseph Lipsick, and colleagues (Stanford University, Stanford, CA).

From S phase to prophase, chromatin must replicate and then condense to prepare for mitosis. In most eukaryotic cells, euchromatin starts the process by replicating first, but it is the last to condense. Heterochromatin is sandwiched in between, opening for replication and then condensing straightaway.

Proper condensation, the authors find, requires Myb, a fly kinase that regulates S phase. Fly cells lacking Myb divided normally for about a dozen cycles but then began to arrest in prophase with condensation errors. “They start to condense,” says Lipsick, “but they can't finish.”

The failure, the group found, lay in euchromatin. Condensation...

The Rockefeller University Press
2007
The Rockefeller University Press
2007
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