MULTIPLE COPIES OF A BILE ACID-INDUCIBLE GENE IN EUBACTERIUM SP STRAIN VPI-12708
MULTIPLE COPIES OF A BILE ACID-INDUCIBLE GENE IN EUBACTERIUM SP STRAIN VPI-12708
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DOI：
10.1128/jb.172.8.4420-4426.1990
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发表时间：
1990-08-01
影响因子：
3.2
通讯作者：
HYLEMON, PB
中科院分区：
文献类型：
--
作者：
GOPALSRIVASTAVA, R;MALLONEE, DH;HYLEMON, PB
真细菌。VPI 12708菌株是一株具有诱导胆汁酸7-脱羟基活性的厌氧肠道细菌。该菌株经胆酸诱导后产生了几种新的多肽。编码胆汁酸诱导的27,000-Dalton多肽(BaiA1和Bai2)的两个拷贝的基因已经被克隆和测序。我们现在报告这种27,000道尔顿多肽(BaiA3)的第三个拷贝的编码基因。从真细菌DNA的部分Sau3A酶切中克隆到了一个11.2kb碱基的DNA片段。DNA序列分析表明，在27,000道尔顿多肽的编码区内，该基因与该基因100%同源。该基因与另外两个基因在核苷酸水平上有81%的序列同源性。与bai A1和bai A3基因相关的侧翼核苷酸序列在起始密码子的5‘’方向上有930个碱基相同，在终止密码子的3‘’方向上至少有325个碱基相同，包括这两个基因的可能的启动子区域。在与白A1和白A3克隆相关的相同的5‘’区域中发现了额外的开放阅读框架(根据正确的起始密码子，从621到648个碱基对)。白蛋白A1和白蛋白A3基因上游930个碱基的5‘端序列完全不同。该基因是胆汁酸诱导的大操纵子的一部分，在多肽编码区的5‘’或3‘’方向与这两个基因没有同源性，但在5‘’区有一个15个碱基对的核糖体结合位点。这些研究有力地表明，这种细菌中已经发生了基因复制(bai A1和bai A3)，并稳定地保持着这种复制。
Eubacterium sp. strain VPI 12708 is an anaerobic intestinal bacterium which possesses inducible bile acid 7-dehydroxylation activity. Several new polypeptides are produced in this strain following induction with cholic acid. Genes coding for two copies of a bile acid-inducible 27,000-dalton polypeptide (baiA1 and bai2) have been previously cloned and sequenced. We now report on a gene coding for a third copy of this 27,000-dalton polypeptide (baiA3). The baiA3 gene has been cloned in lambda DASH on an 11.2-kilobase DNA fragment from a partial Sau3A digest of the Eubacterium DNA. DNA sequence analysis of the baiA3 gene revealed 100% homology with the baiA1 gene within the coding region of the 27,000-dalton polypeptides. The baiA2 gene shares 81% sequence identity with the other two genes at the nucleotide level. The flanking nucleotide sequences associated with the baiA1 and baiA3 genes are identical for 930 bases in the 5'' direction from the initiation codon and for at least 325 bases in the 3'' direction from the stop condon, including the putative promoter regions for the genes. An additional open reading frame (occypying form 621 to 648 bases, depending on the correct start codon) was found in the identical 5'' regions associated with the baiA1 and baiA3 clones. The 5'' sequences 930 bases upstream from the baiA1 and baiA3 genes was totally divergent. The baiA2 gene, which is part of a large bile acid-inducible operon, showed no homology with the two genes either in the 5'' or 3'' direction from the polypeptide coding region, except for a 15-base-pair presumed ribosome-binding site in the 5'' region. These studies strongly suggest that a gene duplication (baiA1 and baiA3) has occurred and is stably maintained in this bacterium.