OPAL SUPPRESSOR TRNA GENES IN HUMAN, CHICKEN, RABBIT, AND XENOPUS GENOMES

蛋白石抑制基因tRNA序列的进化研究 它们的侧翼序列（即，在人类、兔子、鸡和非洲爪蟾中 基因组）已经完成。 前情提要一只鸡和一个人欧泊 抑制tRNA基因的分离和测序，在过去的一年里， 从兔中分离到的相应基因的序列， 和非洲爪蟾基因组。 人类和兔子的基因 严格保守的鸡和非洲爪蟾;和哺乳动物 基因与其他基因的不同之处在于在位置 11.因此，该基因是高度保守的， 这表明基因产物具有重要的细胞功能。 在 此外，还产生了两种已知形成磷酸丝氨酰-tRNA的基因产物 来自单个蛋白石抑制tRNA基因。 事实上，这些tRNA 在丝氨酸部分磷酸化并读取无义密码子UGA表明 他们有一个专门的和独特的功能， 提出tRNA利用的概念。 tRNA基因产物存在于 与其他丝氨酰-tRNA同种受体相比，在细胞内的水平较低。 5 '端侧翼区，这在兔和人之间高度保守， 和人类基因组，并且在所有四个物种中具有短的同源性， 和5 '端的内部控制区，它有两个额外的核苷酸 与所有已知tRNA基因中的相应片段相比， 在降低蛋白石转录水平中的调节作用 抑制tRNA基因。 这些可能性正在调查， 用另一个tRNA基因的5 '侧翼区替换5'侧翼区， 5 '内部控制区的位点特异性诱变。 已经合成了具有单碱基或双碱基的寡核苷酸 在5 '内部控制区和反密码子的变化， 用于诱变研究，将5 '内部对照区转化为 正常的tRNA控制区，并将蛋白石抑制tRNA基因转化为 赭石抑制剂

An evolutionary study of the sequence of opal suppressor tRNA genes and their flanking sequences (i.e., in human, rabbit, chicken and Xenopus genomes) has been completed. Previously, a chicken and a human opal suppressor tRNA gene were isolated and sequenced and this past year the sequences of the corresponding genes, which had been isolated from rabbit and Xenopus genomes, were determined. The human and rabbit genes are strictly conserved as are those of chicken and Xenopus; and the mammalian genes differ from the others by a single pyrimidine transition at position 11. The gene, therefore, has been highly conserved which provides strong evidence that the gene products have an important cellular function. In addition, two gene products which are known to form phosphoseryl-tRNA arise from the single opal suppressor tRNA gene. The fact that these tRNAs are phosphorylated on the serine moiety and read the nonsense codon UGA suggest that they have a specialized and unique function which lies outside our present concepts of tRNA utilization. The tRNA gene products are present in minor levels intracellularly compared to other seryl-tRNA isoacceptors. Both the 5' flanking region, which has been highly conserved between rabbit and human genomes and has short stretches of homology in all four species, and the 5' internal control region, which has two extra nucleotides compared to the corresponding segment in all known tRNA genes, may have a regulatory role in reducing the level of transcription of the opal suppressor tRNA genes. These possibilities are being investigated by replacing the 5' flanking region with that of another tRNA gene and by site-specific mutagenesis of the 5' internal control region. Oligonucleotides have been synthesized which have a single or double base change in the 5' internal control region and in the anticodon and are being used in mutagenesis studies to convert the 5' internal control region to a normal tRNA control region and to convert the opal suppressor tRNA gene to an ochre suppressor.