Identification of seven genes in the major histocompatibility complex class I region of the zebrafish

Physical linkage of genes whose products are involved in similar physiologi cal pathways may have functional significance. The identification of conser ved gene linkage in distantly related organisms can therefore strengthen th e hypothesis of selection acting towards keeping genes on a chromosome. We used the cDNA selection technique and the polymerase chain reaction (PCR) w ith generic primers for the identification of new genes on the genomic clon es bearing the major histocompatibility complex (Mhc) class I genes of the zebrafish (Danio rerio). We found six new genes (BING1, DAXX, TAPBP, KNSL2, TAP2B and KE6) whose orthologues are known to be linked to the Mhc class I I region in humans and mice. In addition, a new zebrafish Mhc class I gene, termed Dare-UFA, was detected. By contrast, a search for the human leucocy te antigen (HLA)-linked BING3, KE3 and SACM2L genes revealed that these loc i are not located on the class I clones of the zebrafish. The zebrafish cla ss I region contains repetitive elements with similarity to the DANA, SATA and LINE repeats, as well as Tc1 transposable elements. Our findings indica te a high degree of linkage conservation between the zebrafish class I and the mammalian class II regions.