Abstract
Pericentromeric gamma-satellite DNA is organized in constitutive heterochromatin structures. It comprises a 234 bp sequence repeated several thousands times surrounding the centromeric sequence of all murine chromosomes. Potential binding sites for transcription factor Yin Yang 1 (YY1), a repressor or activator of several cellular and viral genes, are present in pericentromeric gamma-satellite DNA. Using gel retardation and chromatin immunoprecipitation, we demonstrate in this work that YY1 specifically interacts in vitro and in vivo with gamma-satellite DNA. Using immunoFISH and confocal microscopy we show that YY1 specifically co-localizes with pericentromeric gamma-satellite DNA clusters organized in constitutive heterochromatin in murine L929 and 3T3 fibroblasts cell lines. Immunoelectron microscopy experiments further confirmed YY1 localization in heterochromatic areas. Overall, our results demonstrate for the first time that a fraction of YY1 is directly associated with constitutive heterochromatin structures. This association appears physiologically relevant since the association of YY1 with pericentromeric gamma-satellite DNA observed in cycling 3T3 fibroblasts strongly diminished in quiescent (G0) 3T3 fibroblasts. We discuss the implications of these results in the context of heterochromatin formation as well as with regard to the YY1-induced repression of euchromatic genes.
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