VARIABILITY IN AN MHCMOSA CLASS-II BETA-CHAIN-ENCODING GENE IN STRIPED BASS (MORONE-SAXATILIS)

The major histocompatibility complex (MHC) class II B locus of the str iped bass (Morone saxatilis) was found to contain multiple forms of th e class II B gene. Seven complete MHC class II B cDNA clones were isol ated and sequenced, identifying five unique allelic forms of a MHC cla ss II B gene. Among three specimens, each representing a geographicall y distinct population (Chesapeake Bay, MD; Roanoke River, NC; and Sant ee-Cooper Reservoir, SC) extensive variability was detected in the bet a(1) encoding domain, which corresponds with the functional peptide-bi nding region (PBR) of known MHC class II molecules. The location of va riable amino acid residues in the beta(1) domains corresponds with pol ymorphic sites observed in other teleosts and higher vertebrates. The amino acid translated beta(2) domain encoding regions, transmembrane r egions, and cytoplasmic regions of the five clones correlated well wit h those of known vertebrate MHC class II proteins. Seventy-one percent of the variability found within the presumed PBR encoded at the MHCMo sa class II B locus corresponded with that of the PBR of a human MHC c lass II B gene. Overall, the Mesa sequences showed greatest similarity to the MHC class II B genes of cichlid fishes, as expected from phylo genetic relationships.