Prothymosin α (ProTα) is an abundant mammalian acidic nuclear protein whose expression is related to cell proliferation. Here we report that in HL-60 cells overexpressing ProTα, the accessibility of micrococcal nuclease to chromatin is strongly increased. In the DNA ladder generated by the nuclease activity, the sizes of the mononucleosome (146 bp, the DNA fragment that is bound to the histone octamer) and its multimers correspond to nucleosomes lacking histone H1. The percentage of histone-H1-depleted chromatin (active chromatin) is also higher in the cells overexpressing ProTα. On the basis of these and previous findings, we propose a biological role for ProTα in the remodelling of chromatin fibres through its interaction with histone H1.

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