Heterochromatic region

Mammalian G9a is a SET-domain histone methyltransferase that methylated H3 at Lys-9 and Lys-27 in vitro and at Lys-9 in vivo [196]. The consensus sequence for G9a appears to be TKXXARKS. G9a is dilferent from Suv39hl is several ways. G9a nuclear localization is distinct from that of Suv39hl, which locate to heterochromatic foci [197]. Suv39hlj2 double mutant mice lose H3 Lys-9 methylation at pericentromeric heterochromatic regions but broad methylation of chromatin remains. It is the latter that is lost in GPa-deficient cells [196]. G9a, molecular mass about 100 kDa, methylates free H3 and nucleosomal H3 with a preference for the former however, the presence of H1 stimulates the methylation of chromatin substrates. Suv39hl, molecular mass about 650 kDa, methylates free H3 and H3 in nucleosomes with equivalent efficiency, but when HI is present, methylation of chromatin substrates is lessened [198]. 

Involved in T cell development. Ikaros proteins target NuRD to heterochromatic regions. [307]... 

Figure.3 Mitotic chromosomes of D. guanche. a) C-banding showing the great amount of heterochromatin on all chromosomes, b) DAPI staining indicates that the heterochromatic regions are AT-rich. c) In situ hybridization with the pGH 290 DNA sequence (see fig.2) proves that this AT-rich sequence constitutes the major part of heterochromatin in this species.

Ohno, S., W. D. Kaplan, and R. Kinosita. 1957. Heterochromatic regions and nucleolus organizers in chromosomes of the mouse,musculus, Exp. Cell Res., 13 358-364. 

Endosperm coloration in maize is governed by an unusual system which has been described by B. McClintock. There are three types of endosperm coloration in corn colorful, colorless, and spotty (color spots on a colorless background). The character of coloration depends upon the interaction between Ac (activator) and Ds (dissociator) genes. These genes control pigment synthesis. Both these controlling elements are located in heterochromatic regions. They could, however, be on different chromosomes. 

The degree of resolution of the banding techniques depends on the degree of elongation of heterochromatic regions. Thus, for all of the banding procedures described below, chromosomes should be prepared according to Protocol 1.2, with the omission of colchicine treatment. 

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