The pub1 E3 ubiquitin ligase negatively regulates leucine uptake in response to NH4+ in fission yeast
The pub1 E3 ubiquitin ligase negatively regulates leucine uptake in response to NH4+ in fission yeast
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DOI：
10.1007/s002940050457
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发表时间：
1999-07-01
期刊：
影响因子：
2.5
通讯作者：
Young, PG
中科院分区：
文献类型：
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作者：
Karagiannis, J;Saleki, R;Young, PG
亮氨酸营养缺陷型的裂变酵母菌株不能在调节至pH 6.4或更高的正常补充的基本培养基中增殖。高pH敏感性可以通过失去Pub 1（一种E3泛素连接酶）或通过用非抑制性氮源（如L-脯氨酸）取代NH 4+来抑制。在这份报告中，我们显示pub 1所需的快速下调观察到的亮氨酸摄取响应添加NH 4+的生长介质。此外，我们证实了较早的结果表明亮氨酸的运输受到负面影响的高细胞外pH值。pub 1是同源的芽殖酵母氮通透酶灭活剂，NP 11/RSP 5，介导的泛素化和随后的破坏NH 4+敏感的通透酶。因此，亮氨酸营养缺陷型细胞的高pH敏感性似乎反映了NH 4+不敏感的渗透酶在质子梯度驱动养分运输较低的条件下无法运输足够的亮氨酸，并且NH 4+敏感的渗透酶已被破坏。有趣的是，部分抑制高pH值的敏感性，和NH 4+对亮氨酸转运的失活作用，看到在pub 1 -1点突变体，成为完整的pub 1三角洲的背景下看到的，当细胞同时失去了spc 1应激激活的MAPK的功能。
Fission yeast strains auxotrophic for leucine are unable to proliferate in normally supplemented minimal media adjusted to pH 6.4 or above. High-pH sensitivity can be suppressed by the loss of Pub1, an E3 ubiquitin ligase, or by the replacement of NH4+ with a non-repressing source of nitrogen such as L-proline. In this report we show pub1 to be required for the rapid down-regulation of leucine uptake observed in response to the addition of NH4+ to the growth media. Furthermore, we corroborate earlier results demonstrating the transport of leucine to be negatively influenced by high extracellular pH. pub1 is homologous to the budding yeast nitrogen permease inactivator, NP11/RSP5, which mediates the ubiquitination and subsequent destruction of NH4+-sensitive permeases. The high-pH sensitivity of cells auxotrophic for leucine thus seems to reflect an inability of NH4+-insensitive permeases to transport sufficient leucine under conditions where the proton gradient driving nutrient transport is low, and NH4+-sensitive permeases have been destroyed. Intriguingly, the partial suppression of both high pH sensitivity, and the inactivating effect of NH4+ on leucine transport, seen in pub1-1 point mutants, becomes as complete as seen in pub1 Delta backgrounds when cells have concomitantly lost the function of the spc1 stress-activated MAPK.