Chromosomal location, exon/intron organization and evolution of lipocalin genes

Lipocalins exhibit low sequence similarity that contrasts with a tightly co nserved folding shared by all members of this superfamily. This conserved f olding can be, at least partly, accounted for by a highly conserved gene st ructure. The array of lipocalin genes that have so far been studied mostly in mammals indicate a large conservation of a typical seven exon/six intron arrangement. Other conserved features include a partly coding exon I of va riable size, fixed sizes of exons 2-5 that code for an array of lipocalin-s pecific beta -strands and a tendency of the last exons to either fuse or ex pand into further exons without major changes in the length of the resultin g open reading frame. The conserved exon/intron arrangement as well as a cl ustering of most lipocalin genes in given chromosomes of human and mouse in dicate that the lipocalin genes diverged from a shared ancestor by successi ve rounds of duplications followed by late changes in exon arrangements. (C ) 2000 Elsevier Science B.V. All rights reserved.