Differential staining in the secondary constriction regions of human chromosomes A1, C9, and E16 by a heat-hypotonic treatment technique.

The secondary constriction (SC) regions of human chromosomes A1, C9, and E16 were preferentially stained with Giemsa when the mitotic cells in a hypotonic solution were heated in a water bath before fixation. The staining intensity of these regions increased from E16 through A1 to C9. The SC region of C9 was stained more intensely as the treatment temperature was raised from 45 degrees C to 60 degrees C, while the staining intensity of the SC region of E16 reached a peak at 50 degrees C and then decreased gradually with increasing temperature. The SC region of A1 showed stable differential staining between 50 degrees C and 60 degrees C. These observations suggest a heterogeneous nature of the SC regions of human chromosomes, probably reflecting a difference in the chromosomal proteins or the DNA-protein interaction in these regions.