PURPLE FISSION YEAST: OVEREXPRESSION and PROCESSING OF THE PIGMENT BACTERIORHODOPSIN IN Schizosaccharomyces pombe*

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Abstract
Abstract– The purple pigment bacteriorhodopsin (BR) acts as a light‐driven proton pump in the cytoplasmic membrane of the archaebacterium Halobacterium halobium. The original gene encoding for the precursor of bacterio‐opsin (bop‐gene) and a shortened gene, where the first nucleotides encoding for the presequence are deleted, were introduced in yeast expression vectors. Northern blot analysis of transformed Schizosaccharomyces pombe cells revealed the strong transcription of the archaebacterial DNA directed by the constitutive alcohol dehydrogenase promoter of the fission yeast. The translated precursor and the second construction without the presequence were accumulated in the plasma membrane fraction of the eukaryote. Yeast cells containing the mature BR showed a weaker color than those harboring the precursor protein, if the cells were grown in minimal medium with 2% glucose. At higher glucose concentrations (7%) the expression of BR increased with and without presequence. The overexpressed precursor leads to coryneform fission yeast, whereas cells transformed with the vector containing the bop‐gene without the presequence, producing the mature protein, retained the rod‐shaped form.