Origin and roles of nuclear matrix proteins. Specific functions of the MAR-binding protein MeCP2/ARBP.

HnRNP proteins are the major protein components of the nuclear matrix, and sites of nascent transcripts and RNA maturation are its main sources. The evidence for and the roles of functional and structural loops in interphase chromatin and metaphase chromosomes is discussed. Recent data suggest a specific role for the matrix attachment region (MAR)- and methyl-CpG-binding protein MeCP2/ARBP. This repressor protein binds to MARs and, through interaction with mSin3A, recruits a corepressor complex containing histone deacetylases. This in turn is thought to generate a localized silenced chromatin structure. Transfection experiments are presented in support of this model.