Chromosomal distribution of rapidly reannealing DNA in Drosophila melanogaster

Cytological hybridization has been used to localize fractions of rapidly reannealing DNA in salivary chromosomes of Drosophila melanogaster. Complementary RNA of high specific activity was transcribed from hydroxyapatite-fractionated rapidly reannealing sequences and from selected buoyant-density fractions of total DNA. It was then hybridized to chromosome squashes after denaturation of DNA in NaOH. Highly "repeated" DNA sequences were detected over much of the chromosome, but were concentrated in chromocentric heterochromatin. A family of sequences with a low percentage of guanosine plus cytidine was highly concentrated in a particular region within the chromo-center. One "euchromatic" region near the tip of chromosome arm 3L also exhibited a concentration of repeated sequences.