High impact information on STP1

• The transcription factor Stp1 is endoproteolytically processed in response to extracellular amino acids by the plasma membrane SPS (Ssy1-Ptr3-Ssy5)-sensor [1].
• The Pro-domain, required for protease maturation, is autolytically cleaved from the catalytic domain but remains associated, forming an inactive protease complex that binds Stp1 [1].
• Processed Stp1, lacking a cytoplasmic retention motif, enters the nucleus and induces amino acid transporter gene expression [1].
• The processing of Stp1p/Stp2p occurs independently of proteasome function and without the apparent involvement of additional components [2].
• In this study, we report that Asi1 is an integral component of the inner nuclear membrane that maintains the latent characteristics of unprocessed Stp1 and Stp2 [3].

Biological context of STP1

• The STP1 ORF contains three putative zinc fingers [4].
• STP1 is an unessential yeast gene involved in the removal of intervening sequences from some, but not all, families of intervening sequence-containing pre-tRNAs [4].
• The STP1 open reading frame (ORF) could encode a peptide of 64,827 Da; however, inspection of putative transcriptional and translational regulatory signals and mapping of the 5' ends of mRNA provide evidence that translation of the STP1 ORF usually initiates at a second AUG to generate a protein of 58,081 Da [4].
• The STP1 locus is located on chromosome IV close to at least two other genes involved in RNA splicing: PRP3 and SPP41 [4].
• One transformant contained a plasmid that encoded an unessential gene, STP1, that in multiple copies enhanced the suppression of SUP4(G37) and caused increased production of mature SUP4(G37) product [5].

Anatomical context of STP1

• A H+/hexose cotransporter (STP1) from Arabidopsis thaliana has been successfully expressed in oocytes and further characterization has shown the transporter to have properties similar to the same transporter expressed in yeast [6].
• Both wild-type STP1 and the recombinant his-tagged protein were located in the plasma membranes of transformed yeast cells [7].

Associations of STP1 with chemical compounds

• Genetic analysis identified five loci, named ssy1 through ssy5. ssy2 corresponds to the previously characterized bap1 mutation, which we recently have found to be allelic to stp1. ssy1, ssy3 and ssy5 exhibit a reduced uptake of phenylalanine, methionine and threonine, as well [8].
• Ssy5 is significantly similar to serine proteases, its self-processing is a prerequisite for Stp1 cleavage, and its overexpression causes inducer-independent Stp1 cleavage and high-level AGP1 transcription [9].
• To investigate this possibility, proton-selective microelectrodes have been used to measure intracellular pH during symport of H+ and hexose in oocytes expressing STP1 [6].
• Stp1 and Stp2 are homologous transcription factors in yeast that are synthesized as latent cytoplasmic precursors with NH2-terminal regulatory domains [3].
• In this work, we use the expression of the low molecular weight tyrosine phosphatase Stp1 from the distantly related yeast Schizosaccharomyces pombe, as a tool to investigate whether an unbalanced level of protein tyrosine phosphorylation affects S. cerevisiae growth and metabolism [10].
• Supporting this notion, a knockout mutant for the STP1 gene was found to be hypersensitive to rapamycin, and overexpression of STP1 conferred resistance to rapamycin [11].

Enzymatic interactions of STP1

• Upon detection of external amino acids, Ssy1-Ptr3 likely allows-in a manner dependent on SCF(Grr1)-the Ssy5 endoprotease to gain access to and to cleave Stp1, this requiring prior phosphorylation of Stp1 by casein kinase I [9].

Regulatory relationships of STP1

• As a simple hypothesis we propose that Stp1p is a transcription factor which activates BAP2, and probably other amino-acid permease genes [12].

Other interactions of STP1

• A 3 kb region from C. glabrata was sequenced that contains homologues of the S. cerevisiae genes TFB3, MRPL28 and STP1 [13].
• STP1, a gene involved in pre-tRNA processing in yeast, is important for amino-acid uptake and transcription of the permease gene BAP2 [12].
• Neither Stp1p nor Leu3p appear to bind to the UASaa, at least in vitro, as judged from gel retardation assays [14].
• One complex is dependent on Stp2p overexpression and the other is formed independently of STP1 or STP2, suggesting that the UAS(aa)is also bound by another factor [15].
• In the yck mutant lacking this kinase, Stp1 is not cleaved and AGP1 is not induced in response to amino acids [9].

References