The ultrastructural morphology of native salivary gland chromosomes of Drosophila melanogaster: the band-interband question.

Native salivary gland chromosomes of Drosophila melanogaster, isolated without exposure to acid fixatives, have been examined in regions 1A-3B, 15A-17B, 19B-20D and 71E-73A and reveal improved aspects of preservation at the ultrastructural level. Three main points emerge: fine bands are well preserved allowing detection of some not recorded in maps made on classical acid-fixed preparations. Structures with the morphology of putative nascent ribonucleoprotein (RNP) particles are apparent in puffs, diffuse bands and virtually all interbands observed. At this level the morphology of native chromosomes is consistent with the hypothesis that all decondensed regions are members of a continuum of transcriptionally active structures. This notion is relevant to data obtained from other approaches to the band-interband question. (iii) Although the chromosomes have not been exposed to 45% acetic acid, at least some of the dark bands represented by the Bridges as doublets in their classical maps contain vacuoles which include putative RNP particles.