Keith G, Heyman T
Institut de Biologie Moléculaire et Cellulaire, CNRS, Strasbourg, France.
Nucleic Acids Res. 1990 Feb 25;18(4):703-10. doi: 10.1093/nar/18.4.703.
Bovine, rabbit and chicken tRNA(Trp) species and tRNA(Trp) packaged in avian myeloblastosis virus were separated and purified using two-dimensional gel electrophoresis and their primary structures were determined. Two major tRNA(Trp) species (1 and 2) were identified in beef and rabbit, two minor ones (3 and 4) in beef and only one minor in rabbit. Their structures differ by 4 nucleotide substitutions located in the D, S and T loops (positions 16, 47, 57 and 59). Species 3 and 4 differ from one another by only one nucleotide at position 2. Differences between tRNA(Trp) species were also observed in the extent of methylation of some nucleotides. Chicken tRNA(Trp) presents only one species similar to the mammalian type 1 tRNA(Trp). In the case of the three studies animals this tRNA could be separated into two subspecies, which differ by a post-transcriptional modification of nucleotide 7 in the acceptor stem: G or m2G. However only the nonmethylated species is used as the primer of DNA-RNA directed retrotranscription since it is only that form which was found in avian retroviruses. The methylation of G to m2G at position 7 could thus prevent the recognition of tRNA(Trp) by retroviral protein(s) responsible for the selective packaging of the primer tRNA(Trp).
利用二维凝胶电泳对牛、兔和鸡的色氨酸转运核糖核酸（tRNATrp）以及包装在禽成髓细胞瘤病毒中的tRNATrp进行了分离和纯化，并测定了它们的一级结构。在牛肉和兔中鉴定出两种主要的tRNATrp种类（1和2），在牛肉中有两种次要的（3和4），而在兔中只有一种次要的。它们的结构在位于D环、S环和T环的4个核苷酸取代处（第16、47、57和59位）存在差异。种类3和4仅在第2位的一个核苷酸上彼此不同。在一些核苷酸的甲基化程度上也观察到了tRNATrp种类之间的差异。鸡的tRNATrp只呈现出一种与哺乳动物1型tRNATrp相似的种类。在这三种研究动物中，这种tRNA可分为两个亚种，它们在受体茎中核苷酸7的转录后修饰上存在差异：G或m2G。然而，只有未甲基化的种类被用作DNA-RNA定向逆转录的引物，因为在禽逆转录病毒中只发现了这种形式。因此，第7位的G甲基化为m2G可能会阻止负责选择性包装引物tRNATrp的逆转录病毒蛋白对tRNATrp的识别。
