Figure 3.

A region encompassing M7 up to M8 contains a putative degradation signal that is recognized from the ER lumenal side. Oocytes were injected with cRNA coding for truncated α-proteins in the absence (A) or presence (B) of cRNA coding for β subunits, treated as described in Figure 1 and immunoprecipitated with an α antibody under denaturing conditions. (A) Truncated M1–7el α-proteins containing P801L/P803L mutations are degraded from the ER lumenal side. (B) β subunits can efficiently stabilize topologically aberrant M1–7el P801L/P803L and M1–8 P801L/P803L α-proteins but not full-length P801L/P803L α subunits. One of three or four representative experiments is shown. Also indicated are putative topology models determined by an RGS assay of α-proteins expressed in the absence or presence of β subunits. The model of full-length P801L/P803L α subunits expressed in the presence of β subunits is not definitively established (Béguin et al., 1998).