Inheritance in mice of the membrane anchor protein egasyn: the Eg locus determines egasyn levels.

Previous studies have suggested that the binding of mouse flucuronidase to endoplasmic reticulum membrane is stabilized by the membrane protein egasyn. Using a radioimmunoassay for egasyn, we have now examined the inheritance of egasyn levels in mice. Mice of the inbred strain C57BL/6J, which have normal levels of microsomal glucuronidase, contained 56 +/- 10 mug egasyn per gram of liver. Mice of the inbred strain YBR, which carry the Eg0 mutation resulting in the absence of microsomal glucuronidase, did not contain detectable levels of egasyn. The F1 progeny of these two strains contained intermediate levels of egasyn, 25 +/- 4 mug egasyn per gram of liver. Progeny from the backcross of these F1 animals to YBR were distributed equally into two discrete phenotypic classes. One class lacked both egasyn and microsomal glucuronidase, while the other class contained 25 +/- 3 mug egasyn per gram of liver and contained normal levels of microsomal glucuronidase. Thus egasyn levels are determined by the Eg locus and show additive inheritance. These results suggest that the Eg gene codes for egasyn and that it is the inability to produce egasyn that results in a deficiency of microsomal glucuronidase in the Eg0 mutant.