Kalirin expression is regulated by multiple promoters.

Kalirin is a multidomain guanine nucleotide exchange factor for small GTPbinding proteins of the Rho family. It is expressed in multiple isoforms that contain different combinations of functional domains and display a complex pattern of expression during brain development. In addition to the isoforms generated through alternative splicing, we have identified multiple transcriptional start sites in rats and humans. These multiple transcriptional start sites result in full-length Kalirin transcripts possessing different 5' ends encoding proteins with differing amino termini. These alternative first exons display different patterns of expression in developing rats and humans and in cultured cells. Most of these alternate first exons lie >100 kb upstream of exon 2 in both rats and humans. Comparisons of the rat and human Kalirin promoter regions reveal numerous shared potential regulatory elements.