Gao Jun, Davidson Mari K, Wahls Wayne P
Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA.
PLoS One. 2009;4(5):e5533. doi: 10.1371/journal.pone.0005533. Epub 2009 May 14.
Stress-activated protein kinases regulate multiple cellular responses to a wide variety of intracellular and extracellular conditions. The conserved, multifunctional, ATF/CREB protein Atf1 (Mts1, Gad7) of fission yeast binds to CRE-like (M26) DNA sites. Atf1 is phosphorylated by the conserved, p38-family kinase Spc1 (Sty1, Phh1) and is required for many Spc1-dependent stress responses, efficient sexual differentiation, and activation of Rec12 (Spo11)-dependent meiotic recombination hotspots like ade6-M26.
METHODOLOGY/PRINCIPAL FINDINGS: We sought to define mechanisms by which Spc1 regulates Atf1 function at the ade6-M26 hotspot. The Spc1 kinase was essential for hotspot activity, but dispensable for basal recombination. Unexpectedly, a protein lacking all eleven MAPK phospho-acceptor sites and detectable phosphorylation (Atf1-11M) was fully proficient for hotspot recombination. Furthermore, tethering of Atf1 to ade6 in the chromosome by a heterologous DNA binding domain bypassed the requirement for Spc1 in promoting recombination.
CONCLUSIONS/SIGNIFICANCE: The Spc1 protein kinase regulates the pathway of Atf1-promoted recombination at or before the point where Atf1 binds to chromosomes, and this pathway regulation is independent of the phosphorylation status of Atf1. Since basal recombination is Spc1-independent, the principal function of the Spc1 kinase in meiotic recombination is to correctly position Atf1-promoted recombination at hotspots along chromosomes. We also propose new hypotheses on regulatory mechanisms for shared (e.g., DNA binding) and distinct (e.g., osmoregulatory vs. recombinogenic) activities of multifunctional, stress-activated protein Atf1.
应激激活蛋白激酶可调节细胞对多种细胞内和细胞外条件的多种反应。裂殖酵母中保守的多功能ATF/CREB蛋白Atf1（Mts1，Gad7）可与CRE样（M26）DNA位点结合。Atf1可被保守的p38家族激酶Spc1（Sty1，Phh1）磷酸化，并且是许多Spc1依赖性应激反应、高效有性分化以及激活Rec12（Spo11）依赖性减数分裂重组热点（如ade6-M26）所必需的。
方法/主要发现：我们试图确定Spc1在ade6-M26热点调节Atf1功能的机制。Spc1激酶对于热点活性至关重要，但对于基础重组则是可有可无的。出乎意料的是，一种缺乏所有11个MAPK磷酸化受体位点且无可检测磷酸化的蛋白（Atf1-11M）在热点重组方面完全 proficient。此外，通过异源DNA结合结构域将Atf1 tether到染色体中的ade6上，绕过了Spc1在促进重组方面的需求。
结论/意义：Spc1蛋白激酶在Atf1与染色体结合的点处或之前调节Atf1促进的重组途径，并且这种途径调节与Atf1的磷酸化状态无关。由于基础重组不依赖Spc1，Spc1激酶在减数分裂重组中的主要功能是将Atf1促进的重组正确定位在染色体上的热点处。我们还提出了关于多功能应激激活蛋白Atf1的共享（如DNA结合）和不同（如渗透调节与重组发生）活性的调节机制的新假设。
