Originally published as Genetics Published Articles Ahead of Print on April 15, 2007.

Genetics, Vol. 176, 877-890, June 2007, Copyright © 2007
doi:10.1534/genetics.107.070342

Yct1p, a Novel, High-Affinity, Cysteine-Specific Transporter From the Yeast Saccharomyces cerevisiae

Jaspreet Kaur and Anand K. Bachhawat1

Institute of Microbial Technology, Sector 39-A, Chandigarh 160 036, India

1 Corresponding author: Institute of Microbial Technology, Sector 39-A, Chandigarh 160 036, India.
E-mail: anand{at}imtech.res.in

Cysteine transport in the yeast Saccharomyces cerevisiae is mediated by at least eight different permeases, none of which are specific for cysteine. We describe a novel, high-affinity, (Km = 55 µM), cysteine-specific transporter encoded by the ORF YLL055w that was initially identified by a combined strategy of data mining, bioinformatics, and genetic analysis. Null mutants of YLL055w, but not of the other genes encoding for transporters that mediate cysteine uptake such as GAP1, GNP1, MUP1, or AGP1 in a met15{Delta} background, resulted in a growth defect when cysteine, at low concentrations, was provided as the sole sulfur source. Transport experiments further revealed that Yll055wp was the major contributor to cysteine transport under these conditions. The contributions of the other transporters became relevant only at higher concentrations of cysteine or when YLL055w was either deleted or repressed. YLL055w expression was repressed by organic sulfur sources and was mediated by the Met4p-dependent sulfur regulatory network. The results reveal that YLL055w encodes the principal cysteine transporter in S. cerevisiae, which we have named YCT1 (yeast cysteine transporter). Interestingly, Yct1p belongs to the Dal5p family of transporters rather than the amino acid permease family to which all the known amino acid transporters belong.