Some of the inducible forms of the heat shock protein 70 (Hsp70) gene
family are encoded in the class m region of the major histocompatibili
ty complex (MHC) of mammals. This study was undertaken to determine wh
ether Hsp70 genes are linked to the MHC of Xenopus, an amphibian last
sharing a common ancestor with mammals 300-350 million years ago. Segr
egation analyses involving seven haplotypes demonstrated the linkage o
f two or three inducible Hsp70 genes to the frog MHC. Another Hsp70 ge
ne is not closely Linked to the MHC. We conclude that the physical ass
ociation of MHC class I and class II genes with Hsp70 genes is ancient
.