Similarity of PEX and NEP genomic structures. ThePEX and NEP coding exons are represented as boxes, and the sizes of the exons are written below each. The numbering of the exons is 1–22 for PEX representing all known exons, and 3–24 for NEP, which has two 5′ exons (not shown) containing solely untranslated sequences. The first exon in each case begins with a start methionine (ATG), and the last exon ends with a stop codon (*). Seven of the equivalent exons are identical in size between the genes (PEX exons 3, 10, 11, 14, 15, 19, and 21 are the same as the equivalent exons in the NEP genes 5, 13, 14, 17, 18, 21, and 23). Above exon boxes are represented various conserved features: (TM) transmembrane domain; (C) cysteine residue; (Z) pentapeptide zinc-binding motif (HEXXH); (E) second zinc-binding motif (ENXADXGG). The three exons following the transmembrane domain exon contain five cysteine residues similarly spaced between PEXand NEP (amino acid residues 54, 59, 77, 85, and 142 inPEX, and 57, 62, 80, 88, and 143 in NEP). One cysteine residue is present in the middle of the gene at position 406 in PEX, and equivalent position 410 in NEP. Similarly, toward the end of the gene cysteine residues are present at 617, 693, 733, and 746 positions in PEX and equivalent positions of 620, 694, 734, and 746 in NEP. A fingerprint for each gene has been generated by classification of the intron interruption of the reading frame at the end of each exon (Sharp 1981): introns lying in between codons (phase 0), introns interrupting a codon between the first and second base (phase 1), and introns interrupting a codon between the second and third base (phase 2). The fingerprints forPEX and NEP are almost identical.
