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首页> 外文期刊>Journal of bacteriology >A cluster of four genes encoding enzymes for five steps in the folate biosynthetic pathway of Streptococcus pneumoniae.
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A cluster of four genes encoding enzymes for five steps in the folate biosynthetic pathway of Streptococcus pneumoniae.

机译：肺炎链球菌叶酸生物合成途径中五个步骤编码酶的四个基因簇。

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Two genes, sulB and sulC, in a folate biosynthetic gene cluster of Streptococcus pneumoniae were identified after determination of the DNA sequence between two previously reported genes, sulA and sulD, in a cloned segment of chromosomal DNA containing a mutation to sulfonamide resistance. The gene products, SulB and SulC, correspond to polypeptides of 49 and 21 kDa, respectively. SulC has GTP cyclohydrolase activity and catalyzes the first step in the folate biosynthetic pathway. SulB apparently has dihydrofolate synthetase activity in that it complements a folC mutant of Escherichia coli and thus catalyzes the last step in the pathway. Prior work showed that SulA, a dihydropteroate synthase, and SulD, a bifunctional enzyme, catalyze three intervening steps. Mapping of the mRNA transcribed from the operon was consistent with its beginning at a promoter with a -35 site (gTGtCc) and an extended -10 site (T-TG-TAaAAT) and its termination at the end of a hairpin structure, which would give a transcript 3,745 nucleotides in length. SulC showed a considerable conservation of sequence by comparison with proven or putative GTP cyclohydrolases from four unrelated species, with 38 to 53% of the residues being identical. A similar comparison of SulB with dihydrofolate synthetases showed an identity of only 26 to 37%. Overall, comparisons of the five folate biosynthetic enzymes in different species suggest that S. pneumoniae is related more closely to other gram-positive bacteria, less closely to eucaryotes, and least closely to the gram-negative E. coli. The varied arrangements of folate biosynthetic genes in different species imply an early evolutionary period of fluidity in genomic rearrangement.
机译：确定肺炎链球菌叶酸生物合成基因簇中的两个基因sulB和sulC，是在确定两个先前报道的基因sulA和sulD之间的DNA序列后，在一个含有磺酰胺抗性突变的染色体DNA克隆片段中确定了该基因的序列。基因产物SulB和SulC分别对应于49 kDa和21 kDa的多肽。 SulC具有GTP环水解酶活性，并催化叶酸生物合成途径的第一步。 SulB显然具有二氢叶酸合成酶活性，因为它补充了大肠杆菌的folC突变体，因此催化了该途径的最后一步。先前的工作表明，二氢蝶呤合酶SulA和双功能酶SulD催化了三个干预步骤。从操纵子转录的mRNA的定位与其在具有-35位点（gTGtCc）和扩展的-10位点（T-TG-TAaAAT）的启动子开始以及在发夹结构末端的终止相一致。给出一个3745个核苷酸的转录本。与来自四个不相关物种的证明或推定的GTP环水解酶相比，SulC显示出相当可观的序列保守性，其中38％至53％的残基是相同的。 SulB与二氢叶酸合成酶的类似比较显示，其同一性仅为26％至37％。总体而言，对不同物种中的五种叶酸生物合成酶的比较表明，肺炎链球菌与其他革兰氏阳性细菌更紧密相关，与真核生物较不紧密相关，而与革兰氏阴性大肠杆菌最不相关。叶酸生物合成基因在不同物种中的不同排列意味着基因组重排的流动性处于早期进化阶段。

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