, Volume 119, Issue 3, pp 227-241

SUV39h-independent association of HP1β with fibrillarin-positive nucleolar regions

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Heterochromatin protein 1 (HP1), which binds to sites of histone H3 lysine 9 (H3K9) methylation, is primarily responsible for gene silencing and the formation of heterochromatin. We observed that HP1β is located in both the chromocenters and fibrillarin-positive nucleoli interiors. However, HP1α and HP1γ occupied fibrillarin-positive compartments to a lesser extent, corresponding to the distinct levels of HP1 subtypes at the promoter of rDNA genes. Deficiency of histone methyltransferases SUV39h and/or inhibition of histone deacetylases (HDACi) decreased HP1β and H3K9 trimethylation at chromocenters, but not in fibrillarin-positive regions that co-localized with RNA polymerase I. Similarly, SUV39h- and HDACi-dependent nucleolar rearrangement and inhibition of rDNA transcription did not affect the association between HP1β and fibrillarin. Moreover, the presence of HP1β in nucleoli is likely connected with transcription of ribosomal genes and with the role of fibrillarin in nucleolar processes.

Communicated by T. Misteli