首页> 美国卫生研究院文献>Journal of Bacteriology >The cbb operons of the facultative chemoautotroph Alcaligenes eutrophus encode phosphoglycolate phosphatase.
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The cbb operons of the facultative chemoautotroph Alcaligenes eutrophus encode phosphoglycolate phosphatase.

机译:兼性化学自养嗜碱生碱菌的cbb操纵子编码磷酸乙醇酸磷酸酶。

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摘要

The two highly homologous cbb operons of Alcaligenes eutrophus H16 that are located on the chromosome and on megaplasmid pHG1 contain genes encoding several enzymes of the Calvin carbon reduction cycle. Sequence analysis of a region from the promoter-distal part revealed two open reading frames, designated cbbT and cbbZ, at equivalent positions within the operons. Comparisons with known sequences suggested cbbT to encode transketolase (TK; EC 2.2.1.1) as an additional enzyme of the cycle. No significant overall sequence similarities were observed for cbbZ. Although both regions exhibited very high nucleotide identities, 93% (cbbZ) and 96% (cbbT), only the chromosomally encoded genes were heterologously expressed to high levels in Escherichia coli. The molecular masses of the observed gene products, CbbT (74 kDa) and CbbZ (24 kDa), correlated well with the values calculated on the basis of the sequence information. TK activities were strongly elevated in E. coli clones expressing cbbT, confirming the identity of the gene. Strains of E. coli harboring the chromosomal cbbZ gene showed high levels of activity of 2-phosphoglycolate phosphatase (PGP; EC 3.1.3.18), a key enzyme of glycolate metabolism in autotrophic organisms that is not present in wild-type E. coli. Derepression of the cbb operons during autotrophic growth resulted in considerably increased levels of TK activity and the appearance of PGP activity in A. eutrophus, although the pHG1-encoded cbbZ gene was apparently not expressed. To our knowledge, this study represents the first cloning and sequencing of a PGP gene from any organism.
机译:位于染色体上和大质粒pHG1上的真人拟南芥H16的两个高度同源的cbb操纵子包含编码加尔文碳还原循环的几种酶的基因。来自启动子远端部分的区域的序列分析显示在操纵子内的相等位置处的两个开放阅读框,称为cbbT和cbbZ。与已知序列的比较表明,cbbT编码转酮醇酶(TK; EC 2.2.1.1)作为周期的另一种酶。没有观察到明显的总体序列相似性的cbbZ。尽管两个区域均显示出非常高的核苷酸同一性,分别为93%(cbbZ)和96%(cbbT),但只有染色体编码的基因在大肠杆菌中异源表达水平很高。观察到的基因产物CbbT(74 kDa)和CbbZ(24 kDa)的分子量与基于序列信息计算的值具有很好的相关性。在表达cbbT的大肠杆菌克隆中,TK活性大大提高,证实了该基因的身份。具有染色体cbbZ基因的大肠杆菌菌株显示了高水平的2-磷酸乙醇酸磷酸酶(PGP; EC 3.1.3.18)的活性,这是自养生物中乙醇酸代谢的关键酶,野生型大肠杆菌中不存在。自养生长过程中对cbb操纵子的抑制导致大肠曲霉的TK活性水平显着提高,而嗜酸性曲霉中PGP活性出现,尽管显然未表达pHG1编码的cbbZ基因。就我们所知,这项研究代表了来自任何生物的PGP基因的首次克隆和测序。

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