Identification and transcription control of fission yeast genes repressed by an ammonium starvation growth arrest

In fission yeast Schizosaccharomyces pombe, ammonium starvation induces a g rowth arrest, a cell cycle exit in G(1) and a further switch to meiosis. Th is process is regulated by the cAMP-dependent protein kinase and the Wis1-d ependent MAP kinase cascade, and downstream transcription factors. In order to understand how cells adapt their genetic programme to the switch from m itotic cycling to starvation, a differential transcript analysis comparing mRNA From exponentially growing and ammonium-starved cells was performed. G enes repressed by this stimulus mainly concern cell growth, ie. protein syn thesis and global metabolism. Comparison of the expression of two of them, the ribosomal proteins Rps6 and TCTP, in many different growing conditions, evidenced a strong correlation, suggesting that their transcriptions are c oordinately regulated. Nevertheless, by repeating the ammonium starvation o n strains constitutively activated for the PKA pathway (Delta cgs1), or una ble to activate the Wis1-dependent MAP kinase pathway (Delta wis1), or with both characteristics (Delta cgs1 + Delta wis1), the transcriptional inhibi tion was found to be governed either by the PKA pathway, or by the Wis1 pat hway, or by both. These results suggest that during the switch from exponen tial growth to ammonium starvation, cell homeostasis is maintained by downr egulating the transcription of the most expressed genes by a PKA and a Wis1 -dependent process. Accession Nos for the S30 and L14 ribosomal protein cDN A sequences are AJ2731 and AJ2732, respectively. Copyright (C) 2000 John Wi ley & Sons, Ltd.