Acetylation of chromosome squashes of Drosophila melanogaster decreases the background in autoradiographs from hybridization with 125I-labeled RNA.

DNA in prepared chromosomes from the larval salivary glands of Drosophila melanogaster was hybridized with 125I-labeled 5S and tRNA from the same organism. Autoradiography revealed that radioactivity was frequently bound to all regions of the slides, masking labeling of the chromosomes. Acetylation of the preparations before hybridization prevented the formation of this background and revealed the specific chromosomal sites.