Cloning of two genes encoding potassium transporters inNeurospora crassaand expression of the corresponding cDNAs inSaccharomyces cerevisiae

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Abstract
TwoNeurospora crassagenes,trk‐1andhak‐1, encode K+transporters that show sequence similarities to the TRK transporters described inSaccharomyces cerevisiaeandSchizosaccharomyces pombe, and to the HAK transporters described inSchwanniomyces occidentalisand barley. TheN. crassaTRK1 and HAK1 transporters expressed by the corresponding cDNAs in atrk1Δ trk2Δmutant ofS. cerevisiaeexhibited a high affinity for Rb+and K+. Northern blot analysis and comparison of the kinetic characteristics of the two transporters in thetrk1Δ trk2Δmutant with the kinetic characteristics of K+uptake inN. crassacells allowed TRK1 to be identified as the dominant K+transporter and HAK1 as a transporter that is only expressed when the cells are K+starved. The HAK1 transporter showed a high concentrative capacity and is identified as the K+–H+symporter described inN. crassa, whereas TRK1 might be a K+uniporter. Although the co‐existence of K+transporters of the TRK and HAK types in the same species had not been reported formerly, we discuss whether this co‐existence may be the normal situation in soil fungi.