PREPARATION AND PROPERTIES OF NUCLEI FROM THE POSTERIOR SILK GLANDS OF THE SILKWORM BOMBYX MORI

An original method to isolate nuclei from the posterior part of the silk glands has been developed. After a collagenase and Triton X-100 treatment, silk glands were filtered through a steel sieve. This step, which is the most efficient one for the purification, is followed by several washings. The preparation of nuclei is fairly pure, RNA: DNA ratio being 0.3 at the end of the whole procedure, and the final DNA recovery quite satisfactory (40-60%). Although chromatin of the purified nuclei is unusually condensed, and in spite of RNase activity, RNA transcription measured in vitro is quantitatively significant (0.01 % of the total DNA). This transcription, resulting from the activity of endogenous RNA polymerases, reaches a maximum when nuclei were extracted from animals on the 4th day of the fifth instar. Differences with results obtained in vivo are discussed.