The submicroscopic structure of synthetically active units in a puff of drosophila hydei giant chromosomes.

Thin sections of nuclei of salivary glands of Drosophila hydei, treated in vitro with vitamin B-6 in the presence of either actinomycin D or 3'deoxyadenosine revealed the morphology of transcription units observed display a definite polarity with respect to the size of the RNP-particles attached to the deoxynucleoprotein matrix. The length of the longest unit observed was approximately 1.5 micronm, which corresponds well with the size of the RNA extracted from isolated puffs and with preliminary measurement of transcription units observed after speeading of the puffs according to the method of Miller and Beatty (1969).