Liu Xiang-Qin, Yang Jing, Meng Qing
Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada.
J Biol Chem. 2003 Nov 21;278(47):46826-31. doi: 10.1074/jbc.M309575200. Epub 2003 Sep 15.
A bacterial ribonucleotide reductase gene was found to encode four inteins and three group II introns in the oceanic N2-fixing cyanobacterium Trichodesmium erythraeum. The 13,650-bp ribonucleotide reductase gene is divided into eight extein- or exon-coding sequences that together encode a 768-amino acid mature ribonucleotide reductase protein, with 83% of the gene sequence encoding introns and inteins. The four inteins are encoded on the second half of the gene, and each has conserved sequence motifs for a protein-splicing domain and an endonuclease domain. These four inteins, together with known inteins, define five intein insertion sites in ribonucleotide reductase homologues. Two of the insertion sites are 10 amino acids apart and next to key catalytic residues of the enzyme. Protein-splicing activities of all four inteins were demonstrated in Escherichia coli. The four inteins coexist with three group II introns encoded on the first half of the same gene, which suggests a breakdown of the presumed barrier against intron insertion in this bacterial conserved protein-coding gene.
在海洋固氮蓝藻红海束毛藻中发现一个细菌核糖核苷酸还原酶基因编码四个内含肽和三个II类内含子。这个13650碱基对的核糖核苷酸还原酶基因被分为八个外显肽或外显子编码序列，它们共同编码一个768个氨基酸的成熟核糖核苷酸还原酶蛋白，该基因序列的83%编码内含子和内含肽。四个内含肽在基因的后半部分编码，每个都有蛋白质剪接结构域和内切核酸酶结构域的保守序列基序。这四个内含肽与已知的内含肽一起，在核糖核苷酸还原酶同源物中定义了五个内含肽插入位点。其中两个插入位点相隔10个氨基酸，且紧邻该酶的关键催化残基。所有四个内含肽的蛋白质剪接活性在大肠杆菌中得到了证实。这四个内含肽与在同一基因前半部分编码的三个II类内含子共存，这表明在这个细菌保守的蛋白质编码基因中，假定的内含子插入屏障被打破。
