Yeast alanine tRNA

FIGURE 12.36 The complete nncleodde sequence and cloverleaf strnctnre of yeast alanine tRNA. 

Yeast alanine tRNA (tRNA 3), the first nucleic acid to be completely sequenced (Fig. 27-11), contains 76 nucleotide residues, 10 of which have modified bases. Comparisons of tRNAs from various species have revealed many common denominators of structure (Fig. 27-12). Eight or more of the nucleotide residues have modified bases and sugars, many of which are methylated derivatives of the principal bases. Most tRNAs have a guanylate (pG) residue at the 5 end, and all have the trinucleotide sequence CCA(3 ) at the 3 end. When... 

C, G, and U residues are modified in most tRNAs (see key). Dihydrouridine (D) is nearly always present in the D loop likewise, ribothymidine (T) and pseudouridine ( k) are almost always present in theT kCG loop. Yeast alanine tRNA, represented here, also contains other modified bases. The triplet at the tip of the anticodon loop base-pairs with the corresponding codon in mRNA. (b) Three-dimensional model of the generalized backbone of all tRNAs. Note the L shape of the molecule. [Part (a) see R. W. Holly et al., 1965, Science 147 1462 part (b) from J. G. Arnez and... 

Yeast alanine tRNA (tRNA ), the first nucleic acid to be completely sequenced (Fig. 27-11), contains 76 nucleotide residues, 10 of which have modified bases. Comparisons of tRNAs from various species have revealed many common denominators of structure (Fig. 

Transfer RNA, tRNA, soluble RNA, sRNA. Low mol wt 23,000-27,000 approx 75-85 nucleotides. Each tRNA is specific for and binds with a particular amino acid more than one may exist for each amino acid. Performs three functions during protein synthesis binds with its specific amino acid recognizes the corresponding codon on mRNA and places the amino acid in the correct position for attach -ment to the polypeptide chain being formed binds the poly -peptide to the ribosome. First determination of total structure of a transfer RNA (yeast alanine tRNA) Holley et aL. Science 147, 1462 (1965). Reviews of structure and function Miura, Specificity in the Structure of Transfer RNA in fVogr, Nucleic Acid Res. Mol. BioL 6, 39-82 (1967) Cramer, Three-Dimensional Structure of tRNA , ibid. 11, 391-421 (1971) Nucleic Acid Sequence Analysis, S. Mandeles (Columbia University Press, New York, 1972) pp 256-280 Nishi-mura, "Transfer RNA Structure and Biosynthesis in MTP Int. Rev. Sci Biochem.. Ser. One vol. 6, K. Burton, Ed. (University Park Press, Baltimore, 1974) pp 289-322 A. Rich, V. L. Raj Bhandary, Ann. Rev. Biochem. 45, 805-860 (1976) P. F. Agris, The Modified Nucleosides of Transfer RNA, IT (A. R. Liss, New York, 1983) 220 pp. 

FIGURE 7.8 Structure of transfer RNA. (a) The cloverleaf diagram of yeast alanine tRNA. T, ribosylthymine T, pseudouridine I, inosine m l, l-methylinosine m G, l-methylguanosine mX3, 2-methylguanosine ... 

For most of the history of mankind, unraveling the nucleotide sequence of even a quite small nucleic acid was a formidable undertaking. Following 7 years of labor, Robert Holley solved the first such structure, that for an alanine tRNA from yeast, in 1961. This molecule contains a linear chain of 76 nucleotides and includes some unusual bases, which actually help in base sequence determination. For this achievement, Holley shared the Nobel Prize in Physiology or Medicine in 1968. 

Figure 29.3. Alanine-tRNA Sequence. The base sequence of yeast alanyl-tRNA and the deduced cloverleaf secondary structure are shown. Modified nucleosides are abbreviated as follows methylinosine (ml), dihydrouridine (UH2),...

Robert Holley first determined the base sequence of a tRNA molecule in 1965, as the culmination ul 7 years of effort, Indeed, his study of yeast alanyl-tRNA provided the first complete sequence of any nucleic acid. This adapter molecule is a single chain of 76 ribonucleotides (Figure 30.2). The 5 terminus is phosphorylated (pCi), whereas the 3 terminus has a free hydroxyl group. T he amino acid-attachment site is the 3 -hydroxyl group of the adenosine residue at the 3 terminus of the molecule. The sequence 5 - IGC-3 in the middle of the molecule is the anticodon, where I is the purine base inosine. It is complementary to 5 -GCC-3, one of the codons for alanine. 

Figure 29-7 (A) Generalized cloverleaf diagram of all tRNA sequences except for initiator tRNAs numbered as in yeast tRNAae (Fig. 5-30). Invariant bases A, C, G, T, U, and semivariant bases Y (pyrimidine base), R (purine base), H (hypermodified purine base). The dotted regions (a, P, variable loop) contain different numbers of nucleotides in various tRNA sequences. See Rich.179 (B) L form of the yeast phenyl-alanine-specific tRNAphe. The structure is the same as that in Fig. 5-31 but has recently been redetermined at a resolution of 0.20 nm.175 The new data revealed the presence of ten bound Mg2+ ions (green circles) as well as bound spermine (green).

Soon after the discovery of RNase Ti, it was suggested (70, 71) that it would become an important tool for the elucidation of nucleotide sequence in RNA. Indeed, since 1962 several workers have tried to use the enzyme for the nucleotide sequence analysis of RNA, especially in highly purified specific tRNA s. Finally, the brilliant research of Holley and his associates in 1965 resulted in the first elucidation of the complete nucleotide sequence of an RNA, alanine specific yeast tRNA, using RNase Ti as a main tool (29). Since then many successful elucidations of nucleotide sequence of various RNA s, using RNase Ti as a main tool, followed, and now the enzyme is well-known as an essential tool for the structural analysis of RNA. 

Figure 10.29 Diagram of tRNA from yeast, specific for alanine. I, inosine V pseudouridine mG, methylguanosine m2G, dimethylguanosine T, ribothymidine hU, dihydrouridine ml, methylinosine.

Figure 29-3. Structure of tRNA. Left sequence and projection of the conformation. The numbering corresponds to the phenyl alanine specific tRN A of yeast. A, Adenyl nucleoside C, cytosyl nucleoside G, guanidyl nucleoside T, thymidyl nucleoside U, uridyl nucleoside. In the case of the pseudouridyl residue the base is joined to the sugar via the C Pu is a purine nucleotide, Py is a pyrimidine nucleotide, and H is what is known as a hypermodified purine nucleotide. The other positions can be taken by any desired nucleotide, but must be complementary in the case of the hydrogen bonds signified by —. w, Wobble base. Right Spatial structure.

FIGURE 25.15 (a) Structure of a tRNA isolated from yeast that has the speoifio function of transferring alanine residues. Transfer RNAs often oontain unusual nuoleosides. PSU = pseudouridine, RT = ribothymidine, Ml = 1 -methylinosine, I = inosine, DMG = A/ -methylguanosine, DHU = 4,5-dihydrouridine, 1 MG = 1 -methylguanosine. (b) The X-ray crystal structure of a phenylalanine-... 

Now in any given cell there are many types of tRNA, usually more than one for each of the 20 protein amino acids. However, not all of them contain IPA. The serine tRNA of yeast, for example, contains IPA whereas alanine and phenylalanine tRNA from the same organism do not. In 1966, Zachau succeeded in localizing precisely the IPA of the serine tRNA of yeast. The IPA is located right next to the anticodon (Fig. 10). According to further investigations the cytokinin seems to be necessary for the attachment of the anticodon to the codon of the mRNA. 

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