The chicken delta-crystallin gene family. Two genes of similar structure in close chromosomal approximation.

delta-Crystallin is a major protein product of the differentiated chicken lens. We have isolated two, non-allelic delta-crystallin genes using a recombinant bacteriophage/chicken genomic DNA library. There appear to be only these two delta-crystallin genes in the haploid chicken genome. Southern hybridization and R-loop analyses indicate that the two genes are oriented on the chromosome with similar 5'-3' polarity. delta 1, arbitrarily designated as the directionally 5' of the two genes, is 6.7 kilobases in length, while delta 2 is 9.2 kilobases. The two delta-crystallin genes are about 4.2 kilobases apart. Structurally, both genes are arranged in a similar and characteristic pattern of 17 exons/16 introns, as judged by electron microscopy. The delta-crystallin gene locus represents a simple model for the study of structural co-evolution and/or functional co-expression of two related genes within a developmentally modulated region of the genome.