Without H1, unruly chromosomes get tangled up during anaphase.

Alinker histone condenses chromosomes so they fit on the mitotic spindle, as shown by Maresca et al. (page 859).

The linker histone H1 seems like an obvious candidate for a condensing activity. But unreplicated sperm chromatids in Xenopus egg extracts look no less condensed when H1 is depleted. The new results suggest that these chromatids do not aptly represent the normal situation. By first replicating the sperm chromatids, the group was able to show that H1 is a condenser.

H1 was enriched on duplicated chromosomes compared with their unreplicated counterparts. It is not clear how H1 is loaded, but it requires passage through interphase, when DNA is replicated. In the absence of H1, other chromosomal proteins, including condensin and cohesin, found their way to chromosomes. But the H1-free chromosomes were longer, failed to align...

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