TaqI digestion reveals fractions of satellite DNAs on human chromosomes

Characterization of the heterochromatic chromosome regions in sheep

In order to elucidate the structural chromosome organization of the heterochromatic regions in sheep, we have used C-banding, silver-staining, sequential CDD technique and restriction endonuclease banding. By these banding techniques we obtained four fractions of repetitive DNA, the autosomal fractions A and B, the C fraction in the X chromosome, and the D fraction in the Y chromosome. Silver staining revealed active nucleolus organizer regions (NOR's) on the telomeric GC-rich areas of chromosomes 1, 2, 3, 4, and 25 which were digested with HaeIII restriction endonuclease.

Counterstained enhancement of TaqI resistant sites after distamycin A/diamidinophenylindole treatment

Numerous selective and differential staining techniques have been used to investigate the hierarchical organisation of the human genome. This investigation demonstrates the unique characteristics that are produced on fixed human chromosomes when sequential procedures involving restriction endonuclease TaqI. distamycin A (DA) and 4',6-diamidino-2-phenylindole (DAPI) are employed. TaqI produces extensive gaps in the heterochromatic regions associated with satellite II and III DNAs of human chromosomes 1, 9, 15, 16 and Y. DA/DAPI selectively highlights, as brightly fluorescent C-bands, the heterochromatin associated with the alpha, beta, satellite II and III DNAs of these chromosomes. When DA and DAPI are used on chromosomes before TaqI digestion, and then stained with Giemsa, the centromeric regions appear to be more resistant, producing a distinct C-banding pattern and gaps in the heterochromatin regions. Sequential use of the DA/DAPI technique after TaqI treatment produces a bright fluorescence on the remaining pericentromeric regions of chromosomes 1, 9, 16 and Y, which also displayed a cytochemically unique banding pattern. This approach has produced specific enhanced chromosomal bands, which may serve as tools to characterize genomic heterochromatin at a fundamental level.

Digestion of centromeric DNA from each human metaphase chromosome by the 6 bp-restriction enzyme StuI

Although 6 bp-restriction endonucleases infrequently cut DNA, we describe in this paper the banding pattern induced by one of them, StuI (AGGCCT), on fixed human chromosomes. This enzyme is the first 6 bp-restriction endonuclease demonstrated to be able to digest human heterochromatin. It causes the extraction of two families of repeated DNA, the alpha satellite DNA and the 3.4 kb HaeIII family (DYZ1). On the other hand, digestions with StuI and with another two enzymes, HinfI and RsaI, have established the distribution of sequences within the heterochromatic block of chromosome 3.

Molecular characterization of the smallest secondary constriction region (qh) of human chromosome 16

We report the smallest secondary constriction region (h) in human chromosome 16. The cytochemical, cytogenetic, and molecular techniques revealed the complex heterogeneity of heterochromatin observed in this region. The heteromorphisms can be found due to the variation in centromeric (c) region alone or in combination with the h region. Routine selective staining techniques fail to differentiate the C region from the h region. However, the fluorescence in situ hybridization technique clearly demonstrated that the centromere of chromosome 16, which is composed of 340-base-pair dimers arranged in a tandem array of 1.7-kb higher-order repeat units, is not heteromorphic in the present case, but other molecular cytogenetic techniques demonstrated the presence of a very small h region. The evolution of heterochromatin of this region is discussed.

Satellite III DNA: regions of extreme endonuclease resistance and inter-individual polymorphism in the Mb size range

Southern analysis of within-gel digested and restricted human cells has revealed very large Satellite III restriction fragments which show clear inter-individual length polymorphism. The Mb and sub-Mb length of these fragments indicate that they arise from regions of heterochromatin which contain homogeneous Satellite III sequences of peculiar resistance to common endonucleases. Based on sequence alone, such regions would be little digested by endonuclease digestion of chromatin in metaphase, regardless of its method of preparation. Polymorphic regions such as these might be expected to stain as part of the C-banding seen in endonuclease treated metaphase chromosomes, and may in part account for inter-individual C-band heteromorphisms.