Protein quality control pathways require AAA+ proteases, such as Clp and Lon. Lon protease maintains UmuD, an important component of the error‐prone DNA repair polymerase (Pol V), at very low levels in E. coli. Most members of the phylum Cyanobacteria lack Lon (including the model cyanobacterium, Synechocystis sp. PCC6803), so maintenance of UmuD at low levels must employ different proteases. We demonstrate that the first 19 residues from the N‐terminus of UmuD (Sug^1‐19) fused to a reporter protein are adequate to trigger complete proteolysis and that mutation of a single leucine residue (L6) to aspartic acid inhibits proteolysis. This process appears to follow the N‐end rule and is mediated by ClpA/P protease and the ClpS adaptor. Additionally, mutations of arginine residues in the Sug^1‐19 tag suggest that the ClpX/P pathway also plays a role in proteolysis. We propose that there is a dual degron at the N‐terminus of the UmuD protein in Synechocystis sp. PCC6803, which is distinct from the degron required for degradation of UmuD in E. coli. The use of two proteolysis pathways to tune levels of UmuD might reflect how a photosynthetic organism responds to multiple environmental stressors.

中文翻译：

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蓝细菌中易于出错的DNA聚合酶的蛋白水解途径的破译

蛋白质质量控​​制途径需要AAA +蛋白酶，例如Clp和Lon。Lon蛋白酶将UmuD（易错DNA修复聚合酶（Pol V）的重要组成部分）维持在非常低的E水平。大肠杆菌。蓝细菌门的大多数成员都缺乏Lon（包括蓝藻模型，Synechocystis sp。PCC6803），因此维持低水平的UmuD必须使用不同的蛋白酶。我们证明了UmuD N端的前19个残基（Sug ^1-19与报道蛋白融合的）足以触发完整的蛋白水解，单个亮氨酸残基（L6）突变为天冬氨酸的突变会抑制蛋白水解。此过程似乎遵循N端规则，并由ClpA / P蛋白酶和ClpS衔接子介导。此外，Sug ^1-19标签中精氨酸残基的突变表明，ClpX / P途径在蛋白水解中也起作用。我们建议在Synechocystis sp。的UmuD蛋白的N末端有一个双德良子。PCC6803，其是从所述降解决定子不同需要在UmuD降解ë。大肠杆菌。使用两种蛋白水解途径来调节UmuD的水平可能反映了光合生物对多种环境胁迫的反应。