The plasma membrane SPS sensor of external amino acids induces
proteolytic activation of the transcription factor Stp1p.
Claes Andreasson, Per O. Ljungdahl
Stockholm Branch, Ludwig Inst Cancer Research, Box 240, Stockholm, S-171
77, SWEDEN
Yeast cells possess a plasma membrane sensor of extracellular amino
acids. This sensor, referred to as the SPS sensor, is a multimeric
complex that initiates metabolic signals in response to extracellular
amino acids. Ultimately the signals transduced by the SPS sensor
modulate the transcription of a discrete set of amino acid metabolizing
genes. Signal transduction occurs independently of amino acid uptake,
thus the SPS sensor functions as a ligand-activated receptor. Stp1p is a
transcription factor that binds to specific sequences in the promoters
of several SPS sensor regulated genes. We have found that Stp1p is
synthesized as an inactive precursor with a negative regulatory domain
located near the amino-terminus. This regulatory domain prevents Stp1p
dependent transactivation of SPS target promoters. In response to
external amino acids, the SPS sensor facilitates the rapid proteolytic
processing of Stp1p. The amino acid induced processing event removes the
negative regulatory domain and activates Stp1p. These results define a
novel signal transduction pathway in yeast.
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