THE MECHANISM OF GIEMSA-BANDING OF MAMMALIAN CHROMOSOMES, WITH SPECIAL ATTENTION TO THE ROLE OF NON-HISTONE PROTEINS

Abstract

Some cytological, biochemical and biophysical studies were made on the G-banding mechanism of chromosomes, using isolated metaphase chromosomes of the Chinese hamster. The results obtained are:1. All G-banding techniques tested cause the loss of certain macromolecules including DNA and proteins, leading to an uneven distribution of chromatin substances. The amounts of such macromolecules resided in the G-banded chromosomes approximate the morphologically estimated genome size of the Giemsa-positive bands.2. The acrylamide gel electrophoresis reveals that the banding procedures remove non-histone proteins of relatively larger molecular sizes.3.The major non-histone proteins reside in the G-banded chromosomes represent relatively small molecules containing a large number of SS bonds.4. The residual G-band chromatin shows higher Tm and hyperchromicities as compared to the extracted one, suggesting that DNA in the former is more stabilized.5. A slight difference in the DNA base composition between the residual and extracted chromatins does not seem to account for the banding mechanism.6. Removal of RNA and histone does not affect the band formation.7. In conclusion, the Giemsa-positive bands represent relatively thermostable chromatins constituting of smaller non-histone protein molecules.