Two distinct sequences control the targeting and anchoring of the mouse P450 1A1 into the yeast endoplasmic reticulum membrane.

We previously expressed mouse P450 1A1 in the yeast S. cerevisiae. In the present study, I describe experiments in which several deletions in the 5' end of the corresponding cDNA were created. The truncated forms were then expressed in yeast cells. Studies of microsomes obtained from transformed yeast show that the signal-sequence is not required in vivo for the integration of mouse P450 1A1 into the endoplasmic reticulum membrane. In addition, the cytochrome deleted for its hydrophobic signal-sequence appears to be enzymatically functional. These results strongly argue for the existence of a second determinant of membrane targeting and binding.