CLONING OF THE GENE ENCODING A PUTATIVE SERINE THREONINE PROTEIN-KINASE WHICH ENHANCES SPERMINE UPTAKE IN SACCHAROMYCES-CEREVISIAE

Polyamine uptake in Saccharomyces cerevisiae was modulated by extracel lular magnesium; in a magnesium-limited medium, polyamine, especially spermine, was overaccumulated into the interior, whose level was then toxic for the growth of this organism (Maruyama, T., Masuda, N., Kakin uma, Y., and Igarashi K. (1994) Biochim. Biophys. Acta 1194, 289-295). Here we isolated a mutant (strain YTM22-8) whose growth was tolerant to spermine in magnesium-limited medium. This mutant was defective in polyamine uptake and did not overaccumulate spermine. From a yeast gen ome library we cloned a gene (POT1) which restored the spermine uptake of this mutant and the sensitivity of the growth to spermine. The nuc leotide sequence of the POT1 gene indicated that it encodes a putative serine/threonine protein kinase and is located on chromosome XI. The results suggest that spermine uptake by this organism is probably regu lated by phosphorylation and dephosphorylation. (C) 1995 Academic Pres s, Inc.