Nucleic Acids Research, 1980, Vol. 8, No. 1 67-84
© 1980
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Nuclear RNA transcripts from Drosophila melanogaster ribosomal RNA genes containing introns
Department of Cellular Biology, Scripps Clinic and Research Foundation La Jolla, CA 92037, USA
Received July 23, 1979.
The transcription of ribosomal genes in a cell line (Kc) derived from female D.melanogaster, has been investigated using hybridization probes prepared from restriction fragments of a cloned rDNA repeat with a 5 kb type I [Wellauer et al. (1978) Cell 14, 269-278] intron. Gels, of nuclear RNA that have been transferred to diazotized paper and hybridized with labelled intron sequences, reveal both large (1-10 kb) transcripts and a discrete 325 base species. Berk-Sharp experiments [(1977) Cell 12, 721-732] reveal large transcripts that are homologous to intron sequences and extend into 28S sequences as well. However, while the abundance of 28S transcripts is about 50,000 copies per nucleus [Clark et al. (1977) Genetics 86, 789-800], these long transcripts are only present at 1-2 copies per nucleus and the 325 base species is only 10 times more abundant. In view of the fact that female cells have about 400 rDNA genes, 49% of which have type I introns, one must conclude either that transcription rarely occurs from the genes containing introns (the majority) or these transcripts are processed unusually rapidly. Transcripts homologous to the "non-transcribed spacer" region have been found, but their abundance is no higher.
*Present address: Department of Pediatrics, University of California at San Diego, La Jolla, CA 92093, USA.
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