Biochemical properties of fat body DNA of the silkworm, Bombyx mori

Some properties of DNA, especially of pupal fat body of the silkworm, Bombyx mori, were studied. Pupal fat body DNA was separated into at least three components called -DNA, β₁-DNA, and β₂-DNA on methylated albumin kieselguhr (MAK) column chromatography. All of these classes of DNA were demonstrated to be pure DNA, neither contaminated nor hybridized with RNA, by their being positive to the diphenylamine reaction, sensitive to DNase, resistant to RNase, and incorporating thymidine-6-³H but not uridine-5-³H. The GC contents calculated from T_m values were around 38 per cent for all of these three components, almost coinciding with that of bulk DNA. But the molecular weight of -DNA, roughly calculated from the sedimentation coefficient on a sucrose density gradient centrifugation was several-fold larger than that of β₁-DNA.

In the pupal stage, fat body DNA was mainly composed of β₁- and β₂-DNA with a minor amount of -DNA, while in larval stage, it consisted only of -DNA. Larval fat body type DNA was observed in the larval silk gland, and in pupal and/or pharate adult tissues like the integument, muscles, and gonads. On the other hand, pupal fat body type DNA was detected in the tissues destined to degenerate or in the process of degeneration, such as pupal silk gland and midgut. These facts indicate that β₁- and β₂-DNA may be the degradation products of -DNA.