Wolf O, Kourides I A, Gurr J A
Laboratory of Molecular Endocrinology, Memorial Sloan-Kettering Cancer Center, New York, New York 10021.
J Biol Chem. 1987 Dec 5;262(34):16596-603.
The gene encoding the beta subunit of mouse thyrotropin (TSH beta) has been isolated from a mouse genomic library, and its nucleotide sequence has been determined. Blot hybridization analysis of restriction enzyme digests of mouse DNA indicates that there is a single mouse TSH beta gene. The gene is 4.8 kilobases in length and contains five exons, which are 27, 47, 41, 163, and 328 base pairs long. Exons 1, 2, and 3 encode only 5'-untranslated mRNA sequences and are separated by introns that are 150 and 380 base pairs long. The protein-coding mRNA sequences are found in exons 4 and 5 and are interrupted by a 460-base pair intron. The position of this intron, between the codons for amino acids 34 and 35, has been conserved in all the known glycoprotein hormone beta subunit genes. Exons 3 and 4 are separated by a large 3.2-kilobase intron. When primer extension analysis, using an oligonucleotide primer complementary to exon 4 sequences, was employed to locate the transcription start site, four products were obtained. Nucleotide sequencing of these products showed that they were derived from separate TSH beta mRNAs that differed in the lengths of their 5'-untranslated regions. These 5'-untranslated mRNA sequences are derived from different combinations of exons 1, 2, and 3, each spliced to exons 4 and 5. The longest 5'-untranslated sequence, 116 nucleotides long, includes exons 1, 2, and 3 and the first base of exon 4; the shorter 5'-untranslated regions, 75, 69, and 28 nucleotides long, arise by splicing out the second and/or the third exon sequences. In contrast to the mouse TSH beta gene, transcription of the rat TSH beta gene from the analogous start site has been reported to give only a single mRNA, with a 5'-untranslated region of 28 nucleotides. Divergence of the mouse and rat TSH beta gene sequences at RNA splice sites can account for the absence of exon 2, but not exon 3, sequences in rat TSH beta mRNA. Primer extension and RNase protection analyses also showed that the mouse TSH beta gene contains a second transcription start site, located 43 base pairs upstream of the first start site, in a position corresponding to that in the rat TSH beta gene. Each start site in the mouse gene is flanked by characteristic TATAA box and CAAT box sequences.(ABSTRACT TRUNCATED AT 400 WORDS)
从小鼠基因组文库中分离出了编码小鼠促甲状腺激素β亚基（TSHβ）的基因，并测定了其核苷酸序列。对小鼠DNA限制性酶切片段的印迹杂交分析表明，小鼠只有一个TSHβ基因。该基因长度为4.8千碱基，包含5个外显子，长度分别为27、47、41、163和328个碱基对。外显子1、2和3仅编码5'-非翻译mRNA序列，它们被长度分别为150和380个碱基对的内含子隔开。蛋白质编码mRNA序列存在于外显子4和5中，并被一个460个碱基对的内含子中断。这个内含子位于氨基酸34和35密码子之间的位置，在所有已知的糖蛋白激素β亚基基因中都保守存在。外显子3和4被一个3.2千碱基的大内含子隔开。当使用与外显子4序列互补的寡核苷酸引物进行引物延伸分析以定位转录起始位点时，得到了4种产物。对这些产物的核苷酸测序表明，它们来自不同的TSHβmRNA，其5'-非翻译区长度不同。这些5'-非翻译mRNA序列来自外显子1、2和3的不同组合，每个组合都与外显子4和5拼接。最长的5'-非翻译序列长116个核苷酸，包括外显子1、2和3以及外显子4的第一个碱基；较短的5'-非翻译区长度分别为75、69和28个核苷酸，是通过去除第二个和/或第三个外显子序列产生的。与小鼠TSHβ基因不同，据报道大鼠TSHβ基因从类似起始位点转录只产生一种mRNA，其5'-非翻译区长28个核苷酸。小鼠和大鼠TSHβ基因序列在RNA剪接位点的差异可以解释大鼠TSHβmRNA中不存在外显子2序列，但不能解释外显子3序列的缺失。引物延伸和核糖核酸酶保护分析还表明，小鼠TSHβ基因包含第二个转录起始位点，位于第一个起始位点上游43个碱基对处，其位置与大鼠TSHβ基因中的相应位置一致。小鼠基因中的每个起始位点两侧都有特征性的TATAA盒和CAAT盒序列。（摘要截断于400字）
