Drosophila maternal and embryo mRNAs transcribed from a single transcription unit use alternate combinations of exons.

We have investigated the organization and transcription of several genes in Drosophila melanogaster which are clustered on an 18-kb cloned DNA fragment (c25) that maps at 99D on the cytogenetic map. Multiple mRNAs, transcribed from genes which lie adjacent to a ribosomal protein ( rp49 ) gene, are present during oogenesis, embryogenesis, or both. At least five mRNAs are transcribed from one of these genes ( EH8 ); three are zygotic transcripts, of which two are blastoderm stage-specific, whereas two others accumulate during oogenesis and are therefore matenal mRNAs. The complex transcription pattern of this gene indicates that alternate usage of protein-coding exons results in the production of different mRNAs with different coding capabilities during oogenesis and embryogenesis. The EH8 transcription unit is framed by genes actively expressed in the adult male fly; thus, the blastoderm stage-specific promoter may be silent although within a region of transcriptionally active chromatin.