[Patterns in the occurrence and the submicroscopic organization of elongated metaphase chromosomes isolated from the...

Chinese hamster metaphase chromosomes were investigated under different conditions of isolation. Light microscopic study demonstrated different forms of stretched chromosomes, from those in which merely a small region is stretched to rope-like structures 20-25 microns long with diameter of about 0.4 micron. The ratio between the number of stretched and of compact chromosomes is dependent on the concentration of bivalent cations, on the pH and temperature of the isolation buffer. A study of the submicroscopic organization of stretched chromosomes revealed lengthwise fibrils that disappeared after the treatment with 0.6 NaCl and staphylococcal nuclease. Distinct aggregates were seen, whose array is maintaining the stretched chromosome structure. It is suggested that stretched chromosomes appear due to the existing in vivo lability of bonds between the main chromosome components involved in organization of chromatin fiber packing. It is proposed that the structure obtains rigidity in the course of isolation with bivalent cations.