Transfer RNA structure

W. Wintermeyer, J. M. Robertson, H. Weidman, and H. G. Zauchau, in Transfer RNA Structure, Properties and Recognition (P. R. Schimmel, D. Soil, and J. N. Abelson, eds.), 445 157, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York (1979). 

Nucleic Acids. Specific enzymes are most important in determining the structure of nucleic acids. This area of research has grown rapidly following the elucidation of the alanine transfer RNA structure in 1965 (81). 

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. 

Transfer RNA Structure (Figure 27.6, Figure 27.7, Figure 4.20, Figure 27.9)... 

Transfer RNA (tRNA) Transfer RNAs are relatively small nucleic acids containing only about 70 nucleotides They get their name because they transfer ammo acids to the ribosome for incorporation into a polypeptide Although 20 ammo acids need to be transferred there are 50-60 tRNAs some of which transfer the same ammo acids Figure 28 11 shows the structure of phenylalanine tRNA (tRNA ) Like all tRNAs it IS composed of a single strand with a characteristic shape that results from the presence of paired bases m some regions and their absence m others... 

RNA structures, compared to the helical motifs that dominate DNA, are quite diverse, assuming various loop conformations in addition to helical structures. This diversity allows RNA molecules to assume a wide variety of tertiary structures with many biological functions beyond the storage and propagation of the genetic code. Examples include transfer RNA, which is involved in the translation of mRNA into proteins, the RNA components of ribosomes, the translation machinery, and catalytic RNA molecules. In addition, it is now known that secondary and tertiary elements of mRNA can act to regulate the translation of its own primary sequence. Such diversity makes RNA a prime area for the study of structure-function relationships to which computational approaches can make a significant contribution. 

In contrast, RNA occurs in multiple copies and various forms (Table 11.2). Cells contain up to eight times as much RNA as DNA. RNA has a number of important biological functions, and on this basis, RNA molecules are categorized into several major types messenger RNA, ribosomal RNA, and transfer RNA. Eukaryotic cells contain an additional type, small nuclear RNA (snRNA). With these basic definitions in mind, let s now briefly consider the chemical and structural nature of DNA and the various RNAs. Chapter 12 elaborates on methods to determine the primary structure of nucleic acids by sequencing methods and discusses the secondary and tertiary structures of DNA and RNA. Part rV, Information Transfer, includes a detailed treatment of the dynamic role of nucleic acids in the molecular biology of the cell. 

Transfer RNA also has a complex secondary structure due to many intrastrand hydrogen bonds. 

Transfer RNA (tRNA) serves as a carrier of amino acid residues for protein synthesis. Transfer RNA molecules also fold into a characteristic secondary structure (marginal figure). The amino acid is attached as an aminoacyl ester to the 3 -terminus of the tRNA. Aminoacyl-tRNAs are the substrates for protein biosynthesis. The tRNAs are the smallest RNAs (size range—23 to 30 kD) and contain 73 to 94 residues, a substantial number of which are methylated or otherwise unusually modified. Transfer RNA derives its name from its role as the carrier of amino acids during the process of protein synthesis (see Chapters 32 and 33). Each of the 20 amino acids of proteins has at least one unique tRNA species dedicated to chauffeuring its delivery to ribosomes for insertion into growing polypeptide chains, and some amino acids are served by several tRNAs. For example, five different tRNAs act in the transfer of leucine into... 

Not all the cellular DNA is in the nucleus some is found in the mitochondria. In addition, mitochondria contain RNA as well as several enzymes used for protein synthesis. Interestingly, mitochond-rial RNA and DNA bear a closer resemblance to the nucleic acid of bacterial cells than they do to animal cells. For example, the rather small DNA molecule of the mitochondrion is circular and does not form nucleosomes. Its information is contained in approximately 16,500 nucleotides that func-tion in the synthesis of two ribosomal and 22 transfer RNAs (tRNAs). In addition, mitochondrial DNA codes for the synthesis of 13 proteins, all components of the respiratory chain and the oxidative phosphorylation system. Still, mitochondrial DNA does not contain sufficient information for the synthesis of all mitochondrial proteins most are coded by nuclear genes. Most mitochondrial proteins are synthesized in the cytosol from nuclear-derived messenger RNAs (mRNAs) and then transported into the mito-chondria, where they contribute to both the structural and the functional elements of this organelle. Because mitochondria are inherited cytoplasmically, an individual does not necessarily receive mitochondrial nucleic acid equally from each parent. In fact, mito-chondria are inherited maternally. 

Ribonucleic acid (RNA) Molecules including messenger RNA, transfer RNA, ribosomal RNA, or small RNA. RNA serves as a template for protein synthesis and other biochemical processes of the cell. The structure of RNA is similar to that of DNA except for the base thymidine being replaced by uracil. 

These bases are not the only ones that occur in nucleic acids. There are many rare bases that are occasionally found in these molecules, particularly in RNA. Perhaps 100 of these are known, in addition to the five common bases. We shall encounter a few of these rare bases in transfer RNA, tRNA, molecules. It is enough to know that they exist. We need not be concerned with their structure or function. 

To say that RNA molecules are single-stranded molecules is not the same as saying that they have no higher-order structures, hi fact they have several. The formation of Watson-Crick complementary base pairs is a driving force for formation of higher-order structures. These include the stem-loop and hairpin secondary structures, as well as more complex tertiary structures. Of particular note, are the complex structures for transfer RNAs, tRNAs. Examples are provided in figure 12.5 (note that there are several nnnsnal bases in these structnres this is typical of tRNAs but not of RNA molecnles in general). These strnctures are intimately related to the function of these molecnles as adaptors in the process of protein synthesis, as developed in the next chapter. 

There are three classes of RNA ribosomal RNA, messenger RNA, and transfer RNA. It is messenger RNA that codes for the structure of proteins. 

Although all tetracyclines have a similar mechanism of action, they have different chemical structures and are produced by different species of Streptomyces. In addition, structural analogues of these compounds have been synthesized to improve pharmacokinetic properties and antimicrobial activity. While several biological processes in the bacterial cells are modified by the tetracyclines, their primary mode of action is inhibition of protein synthesis. Tetracyclines bind to the SOS ribosome and thereby prevent the binding of aminoacyl transfer RNA (tRNA) to the A site (acceptor site) on the 50S ri-bosomal unit. The tetracyclines affect both eukaryotic and prokaryotic cells but are selectively toxic for bacteria, because they readily penetrate microbial membranes and accumulate in the cytoplasm through an energy-dependent tetracycline transport system that is absent from mammalian cells. 

Ogle JM, Brodersen DE, Clemons Jr WM, Tarry MJ, Carter AP, Ramakrishnan V (2001) Recognition of cognate transfer RNA by the 30S ribosomal subunit. Science 292 897-902 Ogle JM, Murphy FV, Tarry MJ, Ramakrishnan V (2002) Selection of tRNA by the ribosome requires a transition from an open to a closed form. Cell 111 721-732 Ogle JM, Carter AP, Ramakrishnan V (2003) Insights into the decoding mechanism from recent ribosome structures. Trends Biochem Sci 28 259-266... 

A similar situation is found in the structure of putrescine diphosphate " (a model system for amine-nucleic acid interactions) which divides into layers of HjPOJ anions bridged by protonated putrescine (1,4-diamino-n-butane) cations. In a real biological system (yeast phenylalanine transfer RNA) phosphate residues are found to be enveloped by the polyamine spermine [NH2(CH2)jNH(CH2)4NH(CH2)jNH2] which again adopts a linear, nonchelating conformation. ... 

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