Genomic organization of the rat alpha(2u)-globulin gene cluster

The alpha(2u)-globulins are a group of similar proteins, belonging to the l ipocalin superfamily of proteins, that are synthesized in a subset of secre tory tissues in rats. The many alpha(2u)-globulin isoforms are encoded by a multigene family that exhibits extensive homology. Despite a high degree o f sequence identity, individual family members show diverse expression patt erns involving complex hormonal, tissue-specific, and developmental regulat ion. Analysis suggests that there are approximately 20 alpha(2u)-globulin g enes in the rat genome. We have used fluorescence in situ hybridization (FI SH) to show that the alpha(2u)-globulin genes are clustered at a single sit e on rat Chromosome (Chr) 5 (5q22-24). Southern blots of rat genomic DNA se parated by pulsed field gel electrophoresis indicated that the alpha(2u)-gl obulin genes are contained on two NruI fragments with a total size of 880 k bp. Analysis of three PI clones containing alpha(2u)-globulin genes indicat ed that the alpha(2u)-globulin genes are tandemly arranged in a head-to-tai l fashion. The organization of the alpha(2u)-globulin genes in the rat as a tandem array of single genes differs from the homologous major urinary pro tein genes in the mouse, which are organized as tandem arrays of divergentl y oriented gene pairs. The structure of these gene clusters may have conseq uences for the proposed function, as a pheromone transporter, for the prote in products encoded by these genes.