RNA genes transfer

Lowe, T.M. and Eddy, S.R. (1 997) tRNAscan-Se a program for improved detection of transfer RNA genes in genomic sequence. Nucleic Acids Research 25, 955-964. 

Sun et al. (1995) applied a three-layer back-propagation network to classify transfer RNA gene sequences according to their source organisms. The evolutionary relationship derived from this study was consistent with those from other methods. 

This family of related RNA molecules likely was generated by gene duplication followed by specialization. A nucleic acid sequence encoding one member of the family was duplicated, and the two copies evolved independently to generate molecules with specificities for different amino acids. This process was repeated, starting from one primordial transfer RNA gene until the 20 (or more) distinct members of the transfer RNA family present in modem organisms arose. 

Lynch M. Mutation accumulation in nuclear, organelle, and prokaryotic transfer RNA genes. Mol Biol Evol 14 914-925, 1997. 

Fig. 1. Electron micrograph of RNA-DNA hybrids made between 21S rRNA and the denatured Haelll fragment showing an insert in the transfer RNA gene, scale bar 0.2 /tm. Inset, interpretation of main figure dotted lines are RNA, solid lines DNA. Micrograph was a generous gift of Arnika Arnberg. From (81.

Stranded DNA can be recognized and in combination with hybridization techniques, genes can be localized on isolated DNA, as has been shown by Bos et al. [8] who presented direct evidence by electron microscopy of RNA-DNA hybrids for an insertion in the transfer RNA gene (Fig. 1). 

Schweizer, E., C. MacKechnie, and H. O. Halvorson. 1969. The redundancy of ribosomal and transfer RNA genes in Saccharomyces cerevisiae. J. Molec. Biol., 40 261-277. 

By relating individual codons of mRNA to the cognate amino acids, tRNA functions as a key bilingual intermediate in the translation of the genetic code. All transfer RNAs are single-stranded molecules about 80 nucleotides long with a common 3 -terminal CCA sequence. Most of the bases are standard but some (e.g., pseudoU, dihydroU, and T) are derived by modification after transcription of the transfer RNA genes. 

The majority of the peptides in mitochondria (about 54 out of 67) are coded by nuclear genes. The rest are coded by genes found in mitochondrial (mt) DNA. Human mitochondria contain two to ten copies of a smaU circular double-stranded DNA molecule that makes up approximately 1% of total ceUular DNA. This mtDNA codes for mt ribosomal and transfer RNAs and for 13 proteins that play key roles in the respiratory chain. The linearized strucmral map of the human mitochondrial genes is shown in Figure 36-8. Some of the feamres of mtDNA are shown in Table... 

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. 

M. Eigen suggested that the primeval forms of tRNA consisted of iterative PurXPyr, thus, for example, GXC triplets. This assumption is present in the title of the publication Transfer-RNA, ein friihes Gen (Transfer RNA, an early gene ) (Eigen and Winkler-Oswatitsch, 1981). As shown above, a nucleotide chain with a repeating pattern naturally leads to the generation of a complementary antiparallel nucleotide sequence ... 

Mitochondrial DNA contains 37 genes, all of which are essential for normal mitochondrial function. Thirteen of these genes provide instructions for making enzymes involved in oxidative phosphorylation. The remaining genes provide instructions for making molecules called transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), which are chemical cousins of... 

Other specialized RNAs, ribosomal RNA (rRNA), transfer RNAs (tRNAs), and small RNA molecules are not translated into protein but have central roles in gene expression and protein synthesis. 

RNAs have a broader range of functions, and several classes are found in cells. Ribosomal RNAs (rRNAs) are components of ribosomes, the complexes that carry out the synthesis of proteins. Messenger RNAs (mRNAs) are intermediaries, carrying genetic information from one or a few genes to a ribosome, where the corresponding proteins can be synthesized. Transfer RNAs (tRNAs) are adapter molecules that faithfully translate the information in mRNA into a specific sequence of amino acids. In addition to these major classes there is a wide variety of RNAs with special functions, described in depth in Part HL... 

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