ORGANIZATION OF THE SALIVARY-GLAND CHROMOSOME AS REVEALED BY THE PATTERN OF INCORPORATION OF H 3 -THYMIDINE

Abstract

Methods of autoradiography, involving incorporation of H3-thymidine in the salivary-gland chromosomes of young developing larvae of D. melanogaster, have been used to determine lateral and linear patterns of organization in fully developed chromosomes. The findings are consistent with a view (1) that DNA occurs as part of a unit, which traverses the bands and extends along the full length of the chromosome; (2) that the unit occupies only a small part of the cross-sectional area of the chromosomes and therefore constitutes a single strand among many; (3) that this entity remains intact during succeeding replications (except for possible interstrand exchanges); and (4) that DNA may not be distributed uniformly along the strands, because radioactivity appears to be concentrated primarily in regions that correspond to the bands.