The structure and organization of lamprin genes: Multiple-copy genes with alternative splicing and convergent evolution with insect structural proteins

Lamprin is a unique structural protein which forms the extracellular matrix of several cartilaginous structures found in the lamprey. Lamprin is nonco llagenous in nature but shows sequence similarities to elastins and to inse ct structural proteins. Here, we characterize the structure and organizatio n of lamprin genes, demonstrating the presence of multiple similar but not identical copies of the lamprin gene in the genome of the lamprey. In at le ast one species of lamprey, Lampetra richardsoni, the multiple gene copies are arranged in tandem in the genome in a head-to-tail orientation. Lamprin genes from Petromyzon marinus contain either seven or eight exons, with ex on 4 being alternatively spliced in all genes, resulting in a total of six different lamprin transcripts. All exon junctions are of class 1,1. An unus ual feature of the lamprin gene structure is the distribution of the 3' unt ranslated region sequence among multiple exons. A TATA box and cap sequence have been identified in upstream sequences in close proximity to the trans cription start site, but no CAAT box could be identified. Sequence and gene structure comparisons between lamprins, elastins, and insect structural pr oteins suggest that the regions of sequence similarity are the result of a process of convergent evolution.