Comparison of the exons of the mouse and human GCNF genes. The upper line of nucleotide sequence shows the murine protein-coding exons and their flanking sequences (AF254815-AF254821). Protein-coding nucleotides are underlined. The lower line of nucleotide sequence shows the corresponding human sequence. Identical nucleotides are highlighted by bold letters. The AG/GT splice signals are shown in italics. mGCNF indicates the deduced mouse protein sequence; hGCNF indicates the deduced human protein sequences; GCNF indicates identical protein sequences. (a) The second exon and its flanking regions. Forty-one out of 42 nucleotides are identical and the flanking splicing signals are conserved. (b) The third exon and its flanking regions. A homologous sequence coding for identical amino acids was found in the human genomic sequence. No human isoform containing this sequence has been reported. The splice donor site shows the typical pyrimidine-rich sequence followed by the sequence 5'-NCAG in both sequences, but the comparison reveals several base transitions. (c) A single splice donor site in the fourth exon coding for the DNA-binding domain is used in all mouse-derived cDNAs described so far. For the human isoform GCNF-2, the corresponding splice site is used, giving rise to a protein containing the sequence ISVSDD instead of the VSVPDD in mouse. Usage of an alternative splice site located 12 bp further downstream gives rise to the shorter isoform GCNF-1. An asparagine (N) is underlined because one of the human cDNA clones codes for a lysine in this position (U64876/NM_001489). (d) Sequences of the fifth exon coding for the carboxy-terminal extension of the DNA-binding domain are highly conserved. (e) The DNA sequence of the sixth exon is highly conserved. An arginine in hGCNF-2b instead of serine results from alternative splice donor sites of the seventh exon. (f) The comparison of the seventh exon reveals three positions where the mouse and the human isoforms diverge. Isoform hGCNF-2b is generated by using a splice donor site located three nucleotides further downstream. The exons coding for the putative α-helices 3 to 6 (g), 7 and 8 (h), 9 and 10 (i), 11 and 12 (j) in the ligand-binding domain are highly conserved. The comparison of the last coding exon in (j) was extended up to the end of the human cDNA sequence of S88309.