Fig. 2

The proposed intron/exon organization of the gene coding for the GRFamide preprohormone-C from H. magnipapillata and H. vulgaris. A. Protein sequences encoded by exons one to ten. The immature neuropeptide sequences are highlighted in red, while the C- and N-terminal cleavage sites are highlighted in blue. Note that the N-terminal peptide cleavage sites are always at the C-terminus of a Glu residue. The gene has ten exons that each code for a fragment of the preprohormone. Exon one codes for the N-terminus of the protein, which also includes the signal sequence. Exons two codes for one copy of Hydra-RFamide-1. Exons three codes for a protein sequence that includes one copy of the non-amidated neuropeptide pQWFSGRFGLX sequence that combines with the XX sequence at the N-terminus of exon four to yield pQWFSGRFGLXXX. Exon four codes for a pQWLSGRFGLX sequence that combines with the XX sequence at the N-terminus of exon five to yield pQWLSGRFGLXXX. This sequence of events continues until exon ten. Exon ten codes for the C-terminus of the protein, which also includes an XX sequence and one copy of Hydra-RFamide-1. B. Intron/exon organization. This genomic organization of the preprohormone-C gene is based on the assumption that H. magnipapillata and H. vulgaris are one species. The genomic organization is supported by our identification of a contig sc4wPfr_569 in the genomic database from H. magnipapillata, containing exons one to eight plus exon ten. Exon nine was found on a different contig sc4wPfr_90. We assume that this was due to a technical problem in the genome sequencing or assembly. All exons are flanked by consensus donor and acceptor splice sites. The possibility of alternative splicing is supported by our findings that different transcripts exist of the preprohormone-C gene: H. magnipapillata transcript-5 contains exons one to ten. H. vulgaris transcript-3 contains exons one, three to seven and exon ten. H. vulgaris transcript-8 contains exon one and exon two. Exon two contains a stop codon, which explains the absence of other exon combinations involving this exon