Analysis of a 26-kb region linked to the Mhc in zebrafish: Genomic organization of the proteasome component beta/transporter associated with antigen processing-2 gene cluster and identification of five new proteasome beta subunit genes

Sequencing of zebrafish (Danio rerio) bacterial artificial chromosome and P 1 artificial chromosome genomic clone fragments and of cDNA clones has led to the identification of five new loci coding for beta subunits of proteaso mes (PSMB). Together with the four genes identified previously, nine PSMB g enes have now been defined in the zebrafish, Six of the nine genes reside i n the zebrafish MHC (Mhc) class I region, four of them reside in a single c luster closely associated with TAP2 on a 26-kb long genomic fragment, and t wo reside at some distance from the fragment. In addition to homologues of the human genes PSMB5 through PSMB9, two new genes, PSMB11 and PSMB12 have been found for which there are no known corresponding genes in humans. The new genes reside in the PSMB cluster in the Mhc. Homology and promoter regi on analysis suggest that the Mhc-associated genes might be inducible by IFN -gamma, The zebrafish class I region contains representatives of three phyl ogenetically distinguishable groups of PSMB genes, X, Y, and Z. It is propo sed that these genes were present in the ancestral PSMB region before Mhc c lass I genes became associated with it.