Structural organization of the human and mouse laminin beta 2 chain genes, and alternative splicing at the 5' end of the human transcript

We have determined the structural organization of the human and mouse genes that encode the laminin beta 2 chain (s-laminin), an essential component of the basement membranes of the neuromuscular synapse and the kidney glomerulus. The human and mouse genes have a nearly identical exon-intron organization and are the smallest laminin chain genes characterized to date, due to the unusually small size of their introns, The laminin beta 2 chain genes of both species consist of 33 exons that span less than or equal to 12 kilobase pairs of genomic DNA. The exon-intron pattern of the laminin beta 2 chain gene is also highly similar to that of the human genes encoding the homologous laminin beta 1 and beta 3 chains. The putative promoter regions of the human and mouse laminin beta 2 chain genes have features characteristic of the promoters of genes that have a limited tissue expression. Considerable conservation of the intron sequences of the mouse and human genes was observed. The first intron of the human gene, located 1 base pair upstream of the translation start codon, contains a non-consensus 5' splice site, This intron was shown to be inefficiently spliced in humans, suggesting that post-transcriptional mechanisms may be involved in the regulation of laminin beta 2 chain gene expression.