Tsao T F, Marzluf G A
Mol Gen Genet. 1976 Dec 22;149(3):347-55. doi: 10.1007/BF00268537.
Neurospora crassa can utilize various purine bases such as xanthine or uric acid and their catabolic products as a nitrogen source. The early purine catabolic enzymes in this organism are regulated by induction and by ammonium repression. Studies were undertaken to investigate purine base transport and its regulation in Neurospora. The results of competition experiments with uric acid and xanthine transport strongly suggest that uric acid and xanthine share a common transport system. It was also shown that the common transport system for uric acid and xanthine is distinct from a second transport system shared by hypoxanthine, adenine and guanine, and apparently also distinct from the transport system(s) for adenosine, cytosine and uracil. Regulation of the uric acid-xanthine transport system and the hypoxanthine-adenine-guanine transport system was studied. The results reveal that the uric acid-xanthine transport system is regulated by ammonium repression, but does not require uric acid induction. Neither ammonium repression nor uric acid induction controls the hypoxanthine-adenine-guanine transport system. A gene, designated amr, which is believed to be a positive regulatory gene for nitrogen metabolism of Neurospora crassa, was found to dramatically affect both the uric acid-xanthine transport system and the hypoxanthine-adenine-guanine transport system. A model for the action of the amr locus as a positive regulatory gene and for the interaction between the amr gene product and its recognition sites will be discussed.
粗糙脉孢菌能够利用各种嘌呤碱，如黄嘌呤或尿酸及其分解代谢产物作为氮源。该生物体中早期的嘌呤分解代谢酶受诱导和铵抑制的调节。开展了研究以调查粗糙脉孢菌中嘌呤碱的转运及其调节。尿酸和黄嘌呤转运的竞争实验结果强烈表明尿酸和黄嘌呤共享一个共同的转运系统。还表明尿酸和黄嘌呤的共同转运系统与次黄嘌呤、腺嘌呤和鸟嘌呤共享的第二个转运系统不同，并且显然也与腺苷、胞嘧啶和尿嘧啶的转运系统不同。研究了尿酸 - 黄嘌呤转运系统和次黄嘌呤 - 腺嘌呤 - 鸟嘌呤转运系统的调节。结果表明尿酸 - 黄嘌呤转运系统受铵抑制调节，但不需要尿酸诱导。铵抑制和尿酸诱导均不控制次黄嘌呤 - 腺嘌呤 - 鸟嘌呤转运系统。发现一个名为amr的基因，它被认为是粗糙脉孢菌氮代谢的正调控基因，对尿酸 - 黄嘌呤转运系统和次黄嘌呤 - 腺嘌呤 - 鸟嘌呤转运系统都有显著影响。将讨论amr基因座作为正调控基因的作用模型以及amr基因产物与其识别位点之间的相互作用。
