Physical mapping of the rat MHC class II genes shows a high level of inter-species conservation.

We report here a pulsed-field gel electrophoresis map of the rat major histocompatibility complex (MHC) class II region. Using probes for the recently discovered Tap-1 and Tap-2 genes and the different MHC class II genes, we found the gene order in the rat MHC (RT1) region to be RT1.H-Tap-1-Tap-2-Bb-Ba-Db-Da. Moreover, the distance between the Tap-1 and the RT1.Da genes is approximately 150 kb. This, together with recent mapping of the RT1 class III region, demonstrates an extensive colinearity in the MHC region of different species.