This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Zollinger, W. D. Articles by Woodward, D. O. Search for Related Content PubMed PubMed Citation Articles by Zollinger, W. D. Articles by Woodward, D. O.

 Previous Article  |  Next Article 

J Bacteriol. 1972 March; 109(3): 1001-1013
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

Comparison of Cysteine and Tryptophan Content of Insoluble Proteins Derived from Wild-Type and mi-1 Strains of Neurospora crassa

^a Department of Biological Sciences, Stanford University, Stanford, California 94305

ABSTRACT

The possibility of an amino acid substitution (cysteine for tryptophan) in a membrane protein of the [mi-1] strain of Neurospora crassa has been investigated in detail by using a double radioactive labeling procedure. Auxotrophic strains of Neurospora having wild-type [+] or [mi-1] cytoplasm have been grown under conditions which result in the specific labeling of protein tryptophan with ³H and protein cysteine with ³⁵S. Although the least soluble 1 to 20% of the [mi-1] mitochondrial membrane protein was usually found to have a higher Cys/Trp ratio (ratio of cysteine plus half-cystine to tryptophan) than the corresponding [+] fraction, it has been shown that these differences were due mainly to the presence of differential amounts of a very insoluble, cysteine-rich (Cys-rich) material. The same Cys-rich material was found in variable amounts in both [+] and [mi-1] cultures, but the concentration was usually higher in the [mi-1] cultures. The Cys-rich material is clearly distinct from "structural protein" on the basis of amino acid composition and appears to have no direct relationship to the [mi-1] phenotype. In the absence of the Cys-rich material, no difference between the Cys/Trp ratios of corresponding [+] and [mi-1] membrane proteins could be detected. We conclude, therefore, that the previously postulated amino acid substitution of cysteine for tryptophan in [mi-1] membrane protein is incorrect.

¹ Present address: Department of Bacterial Diseases, Walter Reed Army Institute of Research, Walter Reed Army Medical Center, Washington, D.C.