Condensation of all human chromosomes in phase G2 and early mitosis can be drastically inhibited by 33258-Hoechst treatment.

Condensation of human chromosomes in phase G2 and early mitosis is inhibited by the fluorochrome 33258-Hoechst. This inhibitory effect is most apparent in primary diploid fibroblasts and lymphoblasts and least pronounced in peripheral blood lymphocytes. Condensation of the human Y chromosome, which contains a large heterochromatic region rich in A-T base pairs, is drastically inhibited by 33258-Hoechst treatment of fibroblasts and lymphoblasts. The difference in sensitivity of human chromosomes in different cell types to 33258-Hoechst probably reflects differences in the cell-membrane permeabilities to 33258-Hoechst.