Structures of Transfer RNAs

FIGURE 2.8 The general structure of transfer RNA (tRNA) showing the phosphodiester backbone as a ribbon, with bases or base pairs projecting from the backbone. (Adapted from Rich, A. [1977]. Three-dimensional structure and biological function of transfer RNA Accounts of Chem. Res., 10, 388-396, copyright 1977, American Chemical Society, with permission from Accounts of Chemical Research.)... 

From A. Rich and S. H. Kim, The three-dimensional structure of transfer RNA, Sci. Amer. 238 52-62, January 1978. Copyright 1978 by Scientific American, Inc. All rights reserved. Reprinted by permission.)... 

Figure 1.33 (a) The hydrogen bonding between uracil and adenine, (b) The two dimensional cloverleaf representation of the structure of transfer RNA (tRNA) showing the hairpin loops in the structure... 

The base-pairing of complementary nucleotides gives the secondary structure of a nucleic acid. In a double-stranded DNA or RNA, this refers to the Watson-Crick pairing of complementary strands. In a single-stranded RNA or DNA, the intramolecular base pairs between complementary base pairs determines the secondary structure of the molecule. For example, the cloverleaf structure of Figure 8-2a gives the secondary structure of transfer RNAs. 

Although the base triplets are of only minor importance in double-stranded nucleic acids, they have a structural role in determining and stabilizing the tertiary structure of transfer RNA, as discussed in Chapter 20. Base quadruplets where two Watson-Crick base pairs are associated as shown in Fig. 16.17 have been invoked to play a role in DNA-DNA aggregation and DNA recombination, but there is no direct evidence for their occurrence. 

Kim S-H (1981) Three-dimensional structure of transfer RNA and its functional implications. Adv Enzymol 46 279- 315... 

Fig. 4.1 The cloverleaf structure of transfer RNA is shown. The main features of the arms are colored the anticodon arm in green that pairs with messenger RNA during translation, The acceptor stem (red) with the protruding CCA-end to which the activated amino acids are attached...

RNA is also used to store genetic information in some viruses (such as HIV, human immunodeficiency virus). RNA differs from DNA in two respects. Firstly, the sugar units in RNA are riboses rather than deoxy-riboses. The second difference is that thymine is replaced by uracil the latter does not possess a methyl group but is otherwise identical. The structure of transfer RNA (t-RNA) is shown in figure 3.19. 

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 35.1 Structure of transfer RNA (tRNA). The 3-D structure (b) is shown schematically and squashed flat in (a) to emphasise base pairing, the acceptor stem and the anticodon Loop. Reproduced from Pratt and Comely (2004) Essential Biochewistiy, John Wiley, New York. 2004 John Wiley Sons. Reprinted with permission of John Wiley Sons, Inc.

The Complex Between mRNA and the Two tRNAs. With no data except the crystal structure of transfer RNA, one can define the range of possible structures for the complex between messenger RNA and the tRNAs at the A- and P-sites, because of two simple facts. First, we know that the two tRNA anticodons are close together, because they interact simultaneously with successive codons on the mRNA. Second, the 3 termini of the two tRNAs are also close together, because the P-site tRNA bears the peptide chain that is to be covalently linked to the amino acid on the A-site tRNA. 

PMR Studies of Secondary and Tertiary Structure of Transfer RNA in Solution... 

Binding to transfer RNA. In vitro, proflavine binds to transfer RNA. As a consequence, the fixation of the activated amino acid in the first step of protein synthesis is partially inhibited. A strong binding process is involved which alters the secondary structure of transfer RNA. This inhibition is certainly part of the molecular basis of the inhibiting action of acridines on protein synthesis. 

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 ... 

Klug, (Sir) Aaron (1926- ) Lithuanian-born British molecular biologist distinguished for his determination of the structure of transfer RNA and for his work on three-dimensional structure of complexes of proteins and nucleic acids. He was awarded the Nobel Prize for chemistry in 1982 for his development of crystallographic electron microscopy and his work on the structures of biologically important nucleic acid-protein complexes. 

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