Activity of the endogenous RNA polymerase on fixed polytene chromosomes

Abstract

Fixed polytene chromosomes can serve as templates for RNA synthesis in situ, using the endogenous chromosomal DNA-dependent RNA polymerase. Labelling is mainly localized in band regions. However, radioactivity can also be found in interbands and puffs similar to that which occurs in vivo. It is also found by this technique that the nucleolar RNA polymerase appears to be active in these preparations and requires Mg 2+ for activity. Since the pattern of the RNA transcribed in situ with the DNA-dependent RNA polymerase from E. coli of native chromosomes differs from that with endogenous RNA polymerase and resembles the one obtained with heat-treated chromosomes, it is suggested that the polymerase from E. coli does not act specifically on eukaryotic chromosomes.