Figure 2. Alternative splicing of Schistosoma mansoni PCS transcripts.

Three different mRNAs are formed by alternative splicing of the SmPCS primary transcript. i) The S. mansoni PCS gene. Exons 1 to 5 are shown as grey boxes, with the coding regions of exons in dark grey and the non coding parts in light grey color, and introns are shown as white boxes. Exon-1 is the 5′ non-coding region for all S. mansoni PCS transcripts. Potential initiator methionines are indicated as M₁, M₂, and M3. The stop codon, shown as a star (★), is same for all transcripts and is located in exon 5. ii) A transcript encoding a potential mitochondrial PCS protein. The start methionine, M₁, is in exon 2. iii) A transcript encoding a potential cytoplasmic PCS protein. Thirty-five nucleotides are spliced out (black box) from exon-2 causing M₁ and the mitochondrial targeting peptide to be present in a different reading frame from the reminder of the protein. The likely initiator methionine for this transcript is shown as M₂ in exon-2. iv) A splice variant that results in the loss of the cysteine in the catalytic triad. In this transcript exon 2 is completely spliced out and exon 1 is directly spliced to exon 3. The predicted initiator methionine, M₃, is present in exon 3 downstream of the catalytic cysteine residue.