Saccharomyces cerevisiae amino acid permeases

Two additional permeases from Saccharomyces cerevisiae share lower homologies with this family of transporters. One of them is the UGA4 GABA-specific permease ([49], Fig. 2 and Andre, Hein, Grenson and Jauniaux, submitted) the second is the CTR choline transporter [50]. About 19% of the amino acid residues of these two proteins are identical. They show about 10% identity with each of the six amino acid permeases mentioned above. This identity does not include most of the amino acids which are highly conserved among the six permeases. 

The regulation of NCR-sensitive amino acid transporters in Saccharomyces cerevisiae has many points in common with that of catabolic enzymes. Amino acid permeases, as well as some other transporters of nitrogenous nutrients, are integrated into the regulatory circuits, both general and specific, which control catabolic processes. 

Regenberg, B., During-Olsen, L., Kielland-Brandt, M. C., Hohnberg, S. (1999) Substrate specificity and gene expression of the amino-acid permeases in Saccharomyces cerevisiae. Current Genetics, 5(5,317-328. 

The accumulation of a number of amino acids from the external medium seems almost irreversible in Saccharomyces cerevisiae. The first detailed study of this phenomenon concerned histidine [13]. Histidine uptake by the specific histidine permease HlPl is an energy dependent process which accumulates free and intact... 

Interesting as it is, the study of transporters for amino acids and other nitrogenous nutrients in Saccharomyces cerevisiae is a tricky field. Many difficulties must be circumvented to avoid trivial errors. These practical problems are linked with several features of eukaryotic uptake systems, the first being the multiplicity of permeases which transport a given substrate. In relation to this, a major point is to make certain that one is not studying more than one uptake system at a time, and this can hardly be done without genetics. Once individual uptake systems have been identified and separated with the help of genetics, a second difficulty arises, which... 

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