Sequence logo around the ascidian transcription start sites. (A) All the 6312 promoter sequences were aligned around the representative TSSs with consideration of their transcriptional orientation. The pyrimidine-purine (YR) consensus was also observed in the ascidian genome. The TSS is located at position 0. (B) A similar alignment of the 5' ends of the first exons of all the 8753 trans-spliced transcripts is also shown. In this case, the position 0 means the most 5' end of the exons. Splice acceptor sequences, which are replaced with SLs in the trans-splicing reaction, can be observed. The whole replaced sequences are also known as outrons.