In the fission yeast Schizosaccharomyces pombe the Wak1p/ Win1p-Wis1p-Sty1p stress-activated protein kinase (SAPK) pathway relays environmental signals to the transcriptional machinery and modulates gene expression via a cascade of protein phosphorylation. Cells of S. pombe subjected to cold shock (transfer from 28°C to 15°C) transiently activated the Sty1p mitogen-activated protein kinase (MAPK) by phosphorylation. Induction of this response was completely abolished in cells disrupted in the upstream response regulator Mcs4p. The cold-triggered Sty1p activation was partially dependent on Wak1p MAPKKK and fully dependent on Wis1p MAPKK suggesting that the signal transmission follows a branched pathway, with the redundant MAPKKK Win1p as alternative transducer to Wis1p, which subsequently activates the effector Sty1p MAPK. Also, the bZIP transcription factor Atf1p became phosphorylated in a Sty1p-dependent way during the cold shock and this phosphorylation was found responsible for the increased expression of gpd1 + , ctt1 + , tps1 + and ntp1 + genes. Strains deleted in transcription factors Atf1p or Pcr1p were unable to grow upon incubation at low temperature whereas those disrupted in any member of the SAPK pathway were able to do so. These data reveal that S. pombe responds to cold by inducing the SAPK pathway. However, such activation is dispensable for yeast growth in cold conditions, supporting that the presence of Atf1/Pcr1 heterodimers, rather than an operative SAPK pathway, is critical to ensure yeast growth at low temperature by an as yet undefined mechanism.Keywords: cold; SAPK pathway; fission yeast.Low temperature is an important environmental signal for all living organisms. Adaptive response to cold stress involves synthesis of several types of proteins. In bacteria, thermal downshifts induce cold-shock proteins (Csp) that function as RNA chaperones favouring efficient translation of mRNAs at low temperature [1]. However, in eukaryotes no proteins homologous to bacterial Csp's have been isolated and cold shock-inducible proteins range from structural components involved in ribosomal biogenesis to transcriptional regulation factors that activate gene expression in response to a drop in temperature [2,3].The mitogen-activated protein kinase (MAPK) signalling pathways are critical for the sensing and response of eukaryotic cells to changes in the external environment [4]. These MAPK cascades are highly conserved through evolution and serve to transduce signals to the nucleus, which result in new patterns of gene expression [5,6]. Each MAPK module comprises at least three protein kinases: a MAP kinase is activated through phosphorylation on specific threonine and tyrosine residues by a MAPK kinase (MAPKK or MEK) which is in turn activated by phosphorylation in one or several serine and threonine residues by a MAPKK kinase (MAPKKK or MEKK). Recently, different studies have revealed a key role for MAPK cascades in the response of metazoan cells to osmotic changes, heat shock, oxidative stress and UV radi...

Spores from Schizosaccharomyces pombe contain neutral and acid trehalases. When spores from strains disrupted for ntp1(+), which encodes neutral trehalase, were induced to germinate, the onset of the process was markedly delayed as compared to wild-type spores. Further outgrowth was also reduced. Dormant spores lacking neutral trehalase contained twice the amount of trehalose present in wild-type spores and mobilised the intracellular pool of trehalose at a slower rate during germination. Inhibition by phloridzin of the sporulation-specific acid trehalase in ntp1-disrupted spores arrested germination completely while prompting no effect on wild-type spores. These results suggest that the two trehalase enzymes may support the utilisation of trehalose during germination but neutral trehalase is required for a more rapid and efficient process.