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首页> 外文期刊>Journal of bacteriology >Molecular characterization of a negative regulator of Streptococcus sobrinus surface protein antigen gene.
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Molecular characterization of a negative regulator of Streptococcus sobrinus surface protein antigen gene.

机译：链球菌表面蛋白抗原基因负调节剂的分子表征。

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Mutans streptococci have been shown to give rise to variants in terms of expression of surface protein antigens by repeated subculturing of the organisms, which in turn induces changes in colonial morphologies. A 2,850-bp upstream region of the gene (pag) for a surface protein antigen, PAg, of Streptococcus sobrinus MT3791 was determined. Analysis of the nucleotide sequence revealed the existence of three open reading frames (ORFs) located upstream of the pag gene. ORF1 extended from an undetermined further upstream sequence to the termination codon TAG lying 1,943 bp upstream of the pag gene. ORF2, consisting of 609 bp lying 1,689 bp upstream of the pag gene, encoded a protein of 23,347 Da and a protein of 22,792 Da. The synthesis of these proteins (protein antigen regulators) was demonstrated by using the in vitro T7 RNA polymerase/promoter system. ORF3, extending from 314 bp upstream of the pag gene to 712 bp upstream of the pag gene, encoded a protein of 14,802 Da. Disruption of chromosomal ORF2 of parent strain MT3791 by allelic exchange resulted in isogenic mutants, termed PAREm-1 and PAREm-2, that synthesized larger amounts of cell-free and cell-associated PAg than did the parent strain. RNA dot blot analysis demonstrated that expression of PAg-specific mRNA transcripts by mutants PAREm-1 and PAREm-2 was about 32-fold higher than that by strain 3791. Mutants PAREm-1 and PAREm-2 were found to be more hydrophobic than strain MT3791. Resting cells of these mutants attached in larger numbers to saliva-coated hydroxyapatite than did those of the parent strain. These results suggest that protein antigen regulator regulates the expression of PAg gene in a negative fashion, affecting the colonization of tooth surfaces by the organism. Thus, ORF2 is concluded to be a negative regulator gene of PAg synthesis and was designated par.
机译：已经表明，变形菌链球菌通过生物的反复继代培养而在表面蛋白抗原的表达方面产生了变异，这反过来又引起了殖民地形态的变化。确定了链球菌MT3791的表面蛋白抗原PAg的基因（pag）的2,850-bp上游区域。核苷酸序列分析揭示了存在于pag基因上游的三个开放阅读框（ORF）。 ORF1从一个不确定的上游序列延伸到位于pag基因上游1,943 bp处的终止密码子TAG。 ORF2由pag基因上游1689 bp处的609 bp组成，编码一个23,347 Da的蛋白质和22,792 Da的蛋白质。通过使用体外T7 RNA聚合酶/启动子系统，证明了这些蛋白质（蛋白质抗原调节剂）的合成。 ORF3从pag基因上游314 bp延伸到pag基因上游712 bp，编码14,802 Da的蛋白质。通过等位基因交换破坏亲本菌株MT3791的染色体ORF2导致了同基因突变体，称为PAREm-1和PAREm-2，与亲本菌株相比，该突变体合成了大量无细胞和与细胞相关的PAg。 RNA点印迹分析表明，突变体PAREm-1和PAREm-2的PAg特异性mRNA转录表达比菌株3791高约32倍。发现突变体PAREm-1和PAREm-2的疏水性比菌株高MT3791。与亲本菌株相比，这些突变体的静止细胞与唾液包被的羟基磷灰石附着的数量更多。这些结果表明蛋白抗原调节剂以负的方式调节PAg基因的表达，从而影响生物体对牙齿表面的定殖。因此，ORF2被认为是PAg合成的负调控基因，被命名为par。

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