Physical and functional interaction between heterochromatin protein 1alpha and the RNA-binding protein heterogeneous nuclear ribonucleoprotein U.

By combining biochemical purification and mass spectrometry, we identified proteins associated with human heterochromatin protein 1alpha (HP1alpha) both in the nucleoplasm and in chromatin. Some of these are RNA-binding proteins, and among them is the protein heterogeneous nuclear ribonucleoprotein U (hnRNP U)/SAF-A, which is linked to chromatin organization and transcriptional regulation. Here, we demonstrate that hnRNP U is a bona fide HP1alpha-interacting molecule. More importantly, hnRNP U depletion reduces HP1alpha-dependent gene silencing and disturbs HP1alpha subcellular localization. Thus, our data demonstrate that hnRNP U is involved in HP1alpha function, shedding new light on the mode of action of HP1alpha and on the function of hnRNP U.