Structural and functional conservation between the high-affinity K+ transporters of Saccharomyces uvarum and Saccharomyces cerevisiae

In Saccharomyces cerevisiae, high-affinity K+ uptake is dependent upon a 180-kDa plasma membrane protein encoded by TRK1 (c-TRKl) [Gaber étal., Mol. Cell. Biol. 8 (1988) 2848-2859)]. Although hybridization with a c-TRKl probe revealed highly homologous sequences in the genomes of most Saccharomyces species, the TRK1 sequence in S. uvarum (u-TRKl) was detected only under low-stringency conditions. We cloned u-TRKl and found it to confer high-affinity K+ uptake in S. cerevisiae. A comparison of the inferred amino acid sequences reveals 78% identity and 86% similarity between the two high-affinity transporters. The most highly conserved regions are the putative membrane-spanning domains (95% identical), suggesting that the structure of the transmembrane domains is important for high-affinity K+ transport.