Printed in Great Britain © Company of Biologists Limited ULTRASTRUCTURE OF POLYTENE CHROMOSOMES OF DROSOPHILA ISOLATED BY

Drosophila polytene chromosomes prepared by a new micromanipulative procedure, which avoids acid squashing, have been examined at the ultrastrucrural level in the electron micro-scope. Puffs at 2B, 68C, 74EF, 75B and 85EF, have been examined in some detail, along with the chromocentre and various interbands. The ultrastructure of these chromosomes, which have never been exposed to acid protein denaturants, compares favourably with that of classical acid-fixed specimens. Ribonucleoprotein particles in puffs are seen to be organized in linear arrays and evidence is adduced for looped transcription units. Particles with charac-teristic sizes and morphologies are observed near the chromocentre, in puffs and in interbands. In interbands RNP particles and 'superbead'-like chromatin particles may be distinguished. Drosophila polytene chromosomes isolated by micro-manipulation should prove useful for the localization of native chromosomal proteins at an ulrrastructural level