The Saccharomyces cerevisiae amino acid transporter Lyp1 has a broad substrate spectrum

The main mediators for the amino acid uptake in Saccharomyces cerevisiae are the permeases belonging to the yeast amino acid transporter family. Recently, we discovered that members of this family support growth on more amino acids than previously described. Here we study the substrate spectrum of Lyp1, the main transporter responsible for the uptake of lysine in yeast. We show that overexpressed Lyp1 supports growth on alanine, asparagine, leucine, methionine, phenylalanine, serine, and valine when these are provided as the sole source of nitrogen to a strain severely deficient for the uptake of amino acids. We show that alanine and serine compete with lysine for the common transport system, albeit with much lower affinity. Thus, Lyp1 has a much broader substrate spectrum than previously thought, which may be true for many amino acid transporters.