Aberrant splicing and transcription termination caused by P element insertion into the intron of a Drosophila gene.

Insertional mutagenesis screens using the P[lacZ, rosy+] (PZ) transposable element have provided thousands of mutant lines for analyzing genes of varied function in the fruitfly, Drosophila melanogaster. As have been observed with other P elements, many of the PZ-induced mutations result from insertion of the P element into the promoter or 5' untranslated regions of the affected gene. We document here a novel mechanism for mutagenesis by this element. We show that sequences present within the element direct aberrant splicing and termination events that produce a mRNA composed of 5' sequences from the mutated gene (in this case, pipsqueak) and 3' sequences from within the P[lacZ, rosy+] element. These truncated RNAs could yield proteins with dominant mutant effects.