Khan A U, Lal S K, Ahmad M
Department of Biochemistry, Faculty of Life Sciences, Aligarh Muslim University, India.
Biochem Biophys Res Commun. 1998 Jan 6;242(1):10-5. doi: 10.1006/bbrc.1997.7553.
The nrdB gene of bacteriophage T4 codes for the small subunit of ribonucleotide reductase and contains a 598-base-pair self-splicing intron which is closely related to other group I introns of T4 and eukaryotes. The screening, isolation, and mapping of 31 nrdB intron mutations were conducted by the strategic usage of the white halo phenotype exhibited by T4 mutants defective in dyhydrofolate reductase or thymidylate synthase. These intron mutations cluster towards the ends, mainly the 3' end, and show a defect in self-splicing. These mutations map in regions of conserved structural elements, thus supporting secondary structure predictions. A distinct pattern of clustering is observed with the highest number of mutations mapping within three of the smaller regions (A, C, and D) of the nrdB intron and no mutations mapping in the largest (B) region. The highest density of mutations mapped in the smallest region (C) of the intron, containing only 96 bases, thus showing a distinct pattern of clustering within the catalytic core.
噬菌体T4的nrdB基因编码核糖核苷酸还原酶的小亚基，并包含一个598个碱基对的自我剪接内含子，该内含子与T4和真核生物的其他I类内含子密切相关。通过策略性地利用二氢叶酸还原酶或胸苷酸合成酶缺陷的T4突变体所表现出的白色晕圈表型，对31个nrdB内含子突变进行了筛选、分离和定位。这些内含子突变集中在末端，主要是3'端，并且显示出自我剪接缺陷。这些突变定位在保守结构元件区域，从而支持二级结构预测。观察到一种独特的聚类模式，在nrdB内含子的三个较小区域（A、C和D）内定位的突变数量最多，而在最大区域（B）内没有突变定位。突变的最高密度定位在内含子的最小区域（C），该区域仅包含96个碱基，因此在催化核心内显示出独特的聚类模式。
