[Cloning and study of inserted sequences of gene 28S in Drosophila melanogaster ribosomal RNA]

Abstract

Cloning of fragments of ribosomal genes containing insertions in the 28S RNA gene has been reported earlier. Subcloning of DNA fragments corresponding to insertion sequences and their hybridization with DNA, RNA and polytene chromosomes from different flies is described. Type 1 insertions (containing BamI sites) are highly heterogeneous in length and sequence even in homozygotes. Type 2 insertions (with EcoRI sites) are rather homogeneous. Two types of insertions are represented in the D. melanogaster genome by 50 and 30 copies, respectively. Restriction fragments with insertions significantly differ in DNA from embryos and larvae. D. simulans and D. virilis also contain the sequences of both types of insertions, though in fewer number of copies. Type 1 insertions seem to be poorly transcribed, and type 2 insertions are not transcribed at all. Among 2000 recombinant clones screened a number of DI plasmids hybridizing to isolated insertions were obtained. Six of them were mapped with restriction endonucleases and hybridized with insertion fragments. rRNA and polytene chromosomes. All of these DI plasmids hybridize with the nucleoli, one with the chromocenter and one with the 79F 3L site. In LI9, not coding for rRNA, the sequences, corresponding to two types on insertions are located only a few kilobases apart. D17a does not encode for rRNA, but hybridizes in situ only with the nucleoli.