PARENTAL CONTROL OF POSITION-EFFECT VARIEGATION: I. PARENTAL HETEROCHROMATIN AND EXPRESSION OF THE WHITE LOCUS IN COMPOUND-X DROSOPHILA MELANOGASTER

Abstract

The tritium is on the 4 (thymidine) or 4 and 5 (cytidine) carbon atoms of the pyrimidine nucleus. 20 Mitchell, H. K., personal communication. 21 The transformation of the soft, segmented larval cuticle into the hard, unsegmented cuticle of the prepupa, called the puparium, takes only a few minutes at 250C., J. H., personal communication. 28 Experiments in progress in which one of the glands of a larva was treated with ribonuclease before autoradiographic exposure, have revealed that tritium introduced in cytidine is removed by the enzyme from the puff regions, as well as from the rest of the chromosomes. A very few nuclei contain RNAase resistant label in their chromosomes. Presumably they correspond to the nuclei that incorporated H3-thymidine and have utilized the pyrimidine moiety of the injected cytidine in DNA synthesis. In parallel experiments it was found that deoxyribonuclease does not affect the observed frequency (100 per cent) of nuclei labeled by H'-cytidine. 29 Breuer, M., and C. Pavan, Chromosoma, 7, 371 (1955).