Chicken immunoglobulin mu-chain gene: germline organization and tandem repeats characteristic of class switch recombination.

We have isolated the phage clones covering the region spanning from the heavy (H)-chain joining (J) region to the end of the mu-chain gene of the chicken immunoglobulin (Ig). The distance from JH to the first exon of the mu-chain constant (C) region is approximately 13 kb, and introns between the C region exons measure more than 3 kb. These distances are significantly larger than those of known mu-chain genes. We found a region cross-hybridizing to the switch regions of the mouse C mu and C alpha genes just in front of the first exon of C mu. Partial nucleotide sequencing of this region revealed that this region consists of tandem repeats of pentamers (C/T)(C/A)CAG complementary to the mammalian switch repetitive region. These findings suggest that this region is a good candidate for a class switch region of the mu-chain gene of chicken Ig.