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Agarose-gel electrophoretic analysis was carried out to study the effect(s) of aging on fixed naked DNA as well as on the DNA part of fixed chromosomes. Results show that aging of fixed DNA produces alterations in molecular size; the alteration is more effective in naked DNA than in the DNA part of fixed chromosomes; and the alteration occurs to a greater extent in air-dried DNA than in DNA aged in fixative. Since B-mercaptoethanol is capable of preventing DNA alterations induced by air-drying, oxidative processes are invoked for explaining these findings as well as the effect(s) of aging on fixed cytological preparations.

The influence of incubation buffers and glycerol on the enzyme activity of naked DNA of lambda phage and mouse, and of mouse chromosomal DNA was investigated. The results obtained varied in part from previously known data, but confirmed the importance of these factors in determining the patterns of in situ restriction enzyme digestion so far attributed exclusively to endonuclease activity.