COTRANSLATIONAL INSERTION OF SELENOCYSTEINE INTO FORMATE DEHYDROGENASE FROM ESCHERICHIA-COLI DIRECTED BY A UGA CODON
COTRANSLATIONAL INSERTION OF SELENOCYSTEINE INTO FORMATE DEHYDROGENASE FROM ESCHERICHIA-COLI DIRECTED BY A UGA CODON
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DOI：
10.1073/pnas.84.10.3156
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发表时间：
1987-05-01
影响因子：
11.1
通讯作者：
BOCK, A
中科院分区：
文献类型：
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作者：
ZINONI, F;BIRKMANN, A;BOCK, A
大肠杆菌甲酸脱氢酶(简称甲酸：苄基紫精氧化还原酶，EC 1.2.-.-)的80 kDa硒多肽的结构基因(FdhF)在140位氨基酸残基上含有一个框内UGA密码子。当杂交基因含有UGA密码子时，fdhF的N-末端部分与lacZ之间的基因融合的翻译取决于介质中硒的可用性；当UGA位置上游的fdhF部分与lacZ融合时，这与硒的存在无关。在这两种情况下，转录都不需要硒的存在。通过局部突变，将UGA密码子转化为丝氨酸(UGA)和半胱氨酸(UGC和UGU)密码子。每一个突变都减轻了fdhF mRNA翻译对硒的依赖。在UGA插入的情况下，硒掺入完全取消，当UGA被半胱氨酸密码子取代时，硒掺入减少到约10%。插入UCA产生一个没有活性的fdhF基因产物，而插入UGC和UGU导致多肽活性降低，这是以前称为甲酸氢解酶的系统的组成部分。总之，结果表明，140位的UGA密码子引导硒半胱氨酸共翻译插入到fdhF多肽链中。
The structural gene (fdhF) for the 80-kDa selenopolypeptide of formate dehydrogenase (formate:benzyl viologen oxidoreductase, EC 1.2.-.-) from Escherichia coli contains an in-frame UGA codon at amino acid position 140 that is translated. Translation of gene fusions between N-terminal parts of fdhF with lacZ depends on the availability of selenium in the medium when the hybrid gene contains the UGA codon; it is independent of the presence of selenium when an fdhF portion upstream of the UGA position is fused to lacZ. Transcription does not require the presence of selenium in either case. By localized mutagenesis, the UGA codon was converted into serine (UGA) and cysteine (UGC and UGU) codons. Each mutation relieved the selenium dependency of fdhF mRNA translation. Selenium incorporation was completely abolished in the case of the UGA insertion and was reduced to about 10% when the UGA was replaced by a cysteine codon. Insertion of UCA yielded an inactive fdhF gene product, while insertion of UGC and UGU resulted in polypeptides with lowered activities as components in the system formerly known as formate hydrogenlyase. Altogether the results indicate that the UGA codon at position 140 directs the cotranslational insertion of selenocysteine into the fdhF polypeptide chain.