A novel procaryotic transcriptional regulatory element, AlgP, with a histone H1-like carboxy-terminal domain was identified in Pseudomonas aeruginosa. AlgP is required for transcription of the key biosynthetic gene algD, which is necessary for production of the exopolysaccharide alginate causing mucoidy in P. aeruginosa. Mucoidy is a critical virulence determinant of P. aeruginosa invariably associated with the respiratory infections causing high mortality in cystic fibrosis. Here we show that AlgP and histones H1 both have repeated units of the Lys-Pro-Ala-Ala motif (KPAA) and its variations within their long (over 100 amino acids) carboxy-terminal domains. This region of histone H1 tails has been shown to bind to the linker DNA in eucaryotic chromatin fibers. A synthetic 50-mer peptide consisting of repeats from the AlgP carboxy-terminal domain was found to bind DNA in a mobility shift DNA-binding assay. AlgP is encoded by a gene that contains multiple direct repeats organized as tandem, head-to-tail, 12-base-pair (bp) units overlapping with six highly conserved 75-bp units. The repetitive structure of the algP gene appears to participate in the processes underlying the metastable character of mucoidy in P. aeruginosa. Relatively large DNA rearrangements spanning the region with tandem direct repeats encoding the carboxy-terminal histone H1-like structure of AlgP were detected in several strains upon conversion from the mucoid to the nonmucoid phenotype. The frequency of the detectable algP rearrangements associated with the transition into the nonmucoid state varied from strain to strain and ranged from 0 to 50%. The nonmucoid derivatives with the clearly rearranged chromosomal copy of algP were complemented to mucoidy with plasmids containing algP from P. aeruginosa PAO. When a random collection of mucoid strains, isolated from different cystic fibrosis patients, was analyzed by using polymerase chain reaction, an additional level of strain-dependent sequence variation in algP was observed. Variations in the number of the 12-bp repeats were found; however, they did not appear to influence the mucoid status of the strains examined. Thus, the repeated region of algP appears to be a hot spot for DNA rearrangements and strain-dependent variability.

译文

在铜绿假单胞菌中鉴定了一种新型的原核转录调节元件AlgP,其具有组蛋白H1-like羧基末端结构域。AlgP是关键生物合成基因algD转录所必需的,这对于产生引起铜绿假单胞菌粘液的胞外多糖藻酸盐是必需的。粘液症是铜绿假单胞菌的关键毒力决定因素,总是与引起囊性纤维化高死亡率的呼吸道感染相关。在这里,我们显示了AlgP和组蛋白H1都具有Lys-Pro-Ala基序 (KPAA) 的重复单元及其在其长 (超过100个氨基酸) 羧基末端结构域中的变化。已显示组蛋白H1尾巴的该区域与真核染色质纤维中的接头DNA结合。在迁移率转移DNA结合试验中,发现由来自AlgP羧基末端结构域的重复序列组成的合成50聚体肽结合DNA。AlgP由一个基因编码,该基因包含多个直接重复序列,组织为串联,头对尾,12碱基对 (bp) 单元,与六个高度保守的75 bp单元重叠。algP基因的重复结构似乎参与了铜绿假单胞菌黏液的亚稳态特征的潜在过程。从粘液样转化为非粘液样表型后,在几个菌株中检测到跨越编码AlgP羧基末端组蛋白H1-like结构的串联直接重复序列的区域的相对较大的DNA重排。与过渡到非粘液状态相关的可检测的algP重排的频率因菌株而异,范围为0至50%。具有明显重排的algP染色体拷贝的非粘液衍生物与含有铜绿假单胞菌PAO的algP的质粒互补为粘液。当使用聚合酶链反应分析从不同的囊性纤维化患者中分离出的粘液样菌株的随机集合时,观察到algP中菌株依赖性序列变异的额外水平。发现12 bp重复序列的数量有所变化; 但是,它们似乎并未影响所检查菌株的粘液状态。因此,algP的重复区域似乎是DNA重排和应变依赖性变异性的热点。

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