OVEREXPRESSION OF THE ER-MEMBRANE PROTEIN P-450 CYP52A3 MIMICS SEC MUTANT CHARACTERISTICS IN SACCHAROMYCES-CEREVISIAE

High expression of microsomal cytochrome P-450 CYP52A3 from Candida ma ltosa induces the formation of membrane stacks in Saccharomyces cerevi siae. Membrane proliferation is accompanied by coinduction of the ER p roteins KAR2p and SEC61p and accumulation of precursor forms of protei ns that have to translocate across the ER membrane (KAR2p, alpha facto r). Cytosolic proteins (SSA1p and 2p) and mitochondrial proteins (CYT c(1)p and F-1 beta p) are not affected. N-terminal truncated P-450 pro teins remain in the cytoplasm and fail to induce membrane proliferatio n, KAR2p/SEC61p expression, and precursor accumulation. Membrane and p recursor protein accumulation are typical features of sec mutants. We assume that the high amounts of P-450p block one or more factor(s) of the transport machinery and thereby cause the observed phenomena.