Dynamic organization of the beta-heterochromatin in the Drosophila melanogaster polytene X chromosome

Region 20 of the polytene X chromosome of Drosophila melanogaster was studi ed in salivary glands (SC) and pseudonurse cells (PNC) of otu mutants. In S G chromosomes the morphology of the region strongly depends on two modifier s of position effect variegation: temperature and amount of heterochromatin . It is banded in XYY males at 25 degrees C and beta-heterochromatic in XO males at 14 degrees C, i.e. it shows dynamic transitions. In PNC chromosome s region 20 is not heterochromatic, but demonstrates a clear banding patter n. Some molecular markers of mitotic heterochromatin were localized by mean s of in situ hybridization on PNC chromosomes: DNA of the gene su(f) in sec tion 20C, the nucleolar organizer and 359-bp satellite in 20F. The 359-bp s atellite, which has been considered to be specific for heterochromatin of t he mitotic X chromosome, was found at two additional sites on chromosome 3L , proximally to 80C. The right arm of the X chromosome in SG chromosomes wa s localized in the inversion In(1LR)pn2b: the telomeric HeT-A DNA and AAGAG satellite from the right arm are polytenized, having been relocated from h eterochromatin to euchromatin.