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A. two-gene cluster where the 3' UTR of one gene overlaps with the outron of the next gene downstream. The sequence shows the 3' UTR of F07F6.4, with the site of polyA addition (dotted underline and boldface) and the polyA signal (underlined and in boldface). This site is only eighteen bp upstream of the SL1 trans-splice site of F07F6.8 (double underlined). Presumably a promoter within the F07F6.4 3' UTR results in the synthesis of the F07F6.8 outron. The H3K9ac track shown provides evidence for this promoter. The length of the vertical lines is proportional to the number of reads corresponding to the indicated genomic position. B. Dual use of an exon. This panel shows an example of two genes that overlap. The upstream gene, W09G3.8, ends within the exon shown in the middle of the diagram. The downstream gene, W09G3.2, begins by SL1 trans-splicing at the 5' end of this same exon, as indicated by 555 SL1 transcriptome reads at this site. In this case, it is impossible for a single polycistronic pre-mRNA to give rise to both mRNAs.