Mg 2+-dependent compactness of heterochromatic chromosome segments

Abstract

The stability of heterochromatic blocks in pachytene chromosomes of Tenebrio molitor (Insecta, Coleoptera) was analysed at the chromosomal level using a modified Miller spreading technique. Incubation of nuclei in solutions of different ionic strength and composition revealed that the characteristic compactness of heterochromatic segments was preserved in the presence of at least 0.6 mM MgCl 2. The compactness of these segments was lost in solutions of different ionic strength and composition revealed that the characteristic compactness of heterochromatic segments was preserved in the presence of at least 0.6 mM MgCl 2. The compactness of these segments was lost in solutions containing NaCl (0.1–100 mM), but no MgCl 2. They then resembled the euchromatic segments. The decondensed heterochromatic segments could be recompacted by adding MgCl 2 to a final concentration of 1.0 mM. The characteristic compactness of heterochromatin of pachytene chromosomes therefore depends on the presence of Mg 2+, but is independent of Na +.