Transcription of rDNA insertions in bobbed mutants of Drosophila melanogaster

In Drosophila melanogaster a large number of the genes coding for 18S and 28S rRNA are interrupted in the 28S region by insertions of two types. Ribosomal insertion transcripts were compared in wild-type and bobbed strains. We found that the level of insertion transcripts increased in bobbed mutants after deletion of 50% of INS − genes, and inversely decreased in revertants when more than 50% of wild-type levels. Among type II insertion transcripts we found a predominant 3·5 kb RNA, precisely of the most frequent insertion size. No primary insertion transcript has been found, although it could be undetected if very fast splicing leads to mature 28S occurs.