Reorganization and Expression of Immunoglobulin Genes: Status of Allelic Elements

The formation of productive genes for light-chain and heavy-chain immunoglobulins involves site-specific re-combinations of the germ-line DNA. These recombina-tions result in deletions that juxtapose particular vari-able (V)-region genes to joining (J) elements located upstream from the constant (Q-region genes (Max et al. 1979; Sakano et al. 1979). In the case of heavy chains, subsequent deletions within the multiple CH gene clus-ter can result in a switch from one immunoglobulin class to another (Honjo and Kataoka 1978; Coleclough et al. 1980; Cory et al 1980; Rabbitts et al. 1980). Although lymphoid cells are diploid, only one set of im-munoglobulin alleles are normally expressed, as judged by the production of complete, functional ight or heavy chains (Petals et al. 1965; Weiler 1965). To