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

The α2u-globulins are a group of similar proteins, belonging to the lipocalin superfamily of proteins, that are synthesized in a subset of secretory tissues in rats. The many α2u-globulin isoforms are encoded by a multigene family that exhibits extensive homology. Despite a high degree of sequence identity, individual family members show diverse expression patterns involving complex hormonal, tissue-specific, and developmental regulation. Analysis suggests that there are approximately 20 α2u-globulin genes in the rat genome. We have used fluorescence in situ hybridization (FISH) to show that the α2u-globulin genes are clustered at a single site on rat Chromosome (Chr) 5 (5q22-24). Southern blots of rat genomic DNA separated by pulsed field gel electrophoresis indicated that the α2u-globulin genes are contained on two NruI fragments with a total size of 880 kbp. Analysis of three P1 clones containing α2u-globulin genes indicated that the α2u-globulin genes are tandemly arranged in a head-to-tail fashion. The organization of the α2u-globulin genes in the rat as a tandem array of single genes differs from the homologous major urinary protein genes in the mouse, which are organized as tandem arrays of divergently oriented gene pairs. The structure of these gene clusters may have consequences for the proposed function, as a pheromone transporter, for the protein products encoded by these genes.