Wong Koon Ho, Hynes Michael J, Todd Richard B, Davis Meryl A
Department of Genetics, The University of Melbourne, Melbourne, Vic. 3010, Australia.
Mol Microbiol. 2007 Oct;66(2):534-51. doi: 10.1111/j.1365-2958.2007.05940.x. Epub 2007 Sep 10.
Fungi can use a diverse range of nitrogen sources. Some nitrogen sources sustain a rapid growth rate and are used in preference to less readily metabolized nitrogen sources. The mechanisms involved in this control of nitrogen utilization have been studied in the model filamentous ascomycete, Aspergillus nidulans. The GATA transcription factor AreA is necessary for the expression of nitrogen-catabolic permeases and enzymes. AreA activity is controlled by multiple mechanisms including regulated areA transcript levels and regulated AreA nuclear export. During nitrogen sufficiency, AreA activation is also prevented by the co-repressor NmrA. We have investigated nitrogen signalling to NmrA. NmrA overexpression prevents AreA function irrespective of the nitrogen status. The mRNA levels of areA and nmrA are inversely regulated, suggesting that the relative levels of AreA and NmrA are critical in determining AreA activation. The bZIP transcription factor MeaB was found to activate nmrA expression and a conserved element, TTGCACCAT, bound by MeaB in vitro is present in the promoters of NmrA homologues in other filamentous ascomycetes. Expression of meaB was not strongly regulated suggesting that transcriptional activation by MeaB is modulated by the nitrogen status. This work highlights a new level of complexity in the regulation of nitrogen catabolism.
真菌能够利用多种氮源。一些氮源能维持快速的生长速率，且相较于较难代谢的氮源，它们会被优先利用。在丝状子囊菌模式生物构巢曲霉中，已经对这种氮利用调控所涉及的机制进行了研究。GATA转录因子AreA对于氮分解代谢通透酶和酶的表达是必需的。AreA的活性受多种机制控制，包括调控AreA转录水平和调控AreA的核输出。在氮充足时，共阻遏物NmrA也会阻止AreA的激活。我们已经研究了向NmrA的氮信号传导。无论氮状态如何，NmrA的过表达都会阻止AreA发挥功能。areA和nmrA的mRNA水平呈反向调控，这表明AreA和NmrA的相对水平对于确定AreA的激活至关重要。发现bZIP转录因子MeaB可激活nmrA的表达，并且在体外与MeaB结合的保守元件TTGCACCAT存在于其他丝状子囊菌中NmrA同源物的启动子中。meaB的表达调控并不强烈，这表明MeaB的转录激活受氮状态的调节。这项工作突出了氮分解代谢调控中一个新的复杂层面。
