The phenomenon postulated in FBrf0191875 and FBrf0221514 differs significantly from that annotated in FlyBase as "gene_with_dicistronic_mRNA" (SO:0000722) or "gene_with_polycistronic_transcript" (SO:0000690). The authors postulate that some pairs of genes in D. melanogaster are transcribed as dicistronic pre-mRNAs, that such a pre-mRNA subsequently undergoes an intercistronic cleavage event, and that this cleavage event occurs prior to translation, producing monocistronic mRNAs. Since for gene models we annotate mRNAs, we cannot represent such a scenario at the gene model level.

Currently, the evidence that this type of process occurs in flies is preliminary. The most convincing case made by these authors is for the CheB42a and ppk25 pair. These two genes appear to be transcribed as a dicistronic primary transcript from the upstream CheB42a promoter (supported by RT-PCR of partially spliced primary transcripts and the lack of an apparent promoter for the downstream ppk25 gene). It is postulated that the primary transcript is then cleaved to produce two independent mRNAs (supported by Northern blot). The downstream ppk25 mRNA is translated (as apparent by ribosome profiling) but it lacks a typical 5' cap (determined by RNA immunoprecipitation using an anti-cap antibody).

For the two other gene pairs described (Tektin-C and Bre1, Cdk5 and Flo-1), there are contradicting data: Validated transcription start sites have been mapped to the downstream gene (Bre-1 and Flo-1) as determined by CAGE data (FBrf0213250, FBrf0220331), as well short, capped nascent transcripts indicative of promoter-proximal RNA Polymerase II (FBrf0209722). In one case, modENCODE RNA-Seq data indicate that the downstream gene is expressed in stages and tissues that the upstream gene is not (Tektin-C and Bre-1). These RNA-Seq and TSS data may be viewed on FlyBase GBrowse.