Ribosomal amplification

Weisberg WG, SM Barns, DA Pelletier, DJ Lane (1991) 16S ribosomal DNA amplification for phylogenetic study. J Bacteriol 173 697-703. 

B. Henrion, F. Le Tacon, and F. Maj tin, Rapid identification of genetic variation of ectomycoiThizal fungi by amplification of ribosomal RNA genes. New Phytol. /22 289 (1992). 

Hung, G.-C., Gasser, R.B., Beveridge, I. and Chilton, N.B. (1999a) Species-specific amplification of ribosomal DNA from some species of equine strongyles by PCR. Parasitology 119, 69-80. 

Amplification of DNA of chromosomes. During formation of oocytes parts of the DNA are "amplified" by repeated replication. This provides a way for the ovum to accumulate ribosomal RNA and various proteins in large amounts. Similarly, genes for two abundant proteins of the egg shell or chorion of insects are amplified. Bidirectional replication initiated at discrete positions yields an "onion skin" structure containing many copies of an 90-kb sequence containing the two genes. The polyploidy observed in some highly specialized cells such as the Purkinje cells... 

Translation is an amplification process, in that each molecule of ribosomal protein mRNA can yield many copies of the corresponding protein. 

In vitro selection technology can be used in principle for three tasks. We will discuss these in the following sections for ribosome display, as currently the examples are mostly available from this approach. The first task is to identify a protein or a peptide from a pool of variants. Here, ribosome display is used exclusively as a method for selection, and changes are not actively introduced in the original pool. In this case, proofreading polymerases are used during the PCR amplification steps (see below). A second application is to evolve a given protein or peptide... 

The eukaryotic ribosome display was subsequently used for selection of human antibody scFv fragments binding progesterone from a library prepared from transgenic mice (He etal., 1999). In this case, a proofreading polymerase was used for the PCR amplification steps included in the ribosome display protocol. It was thereby demonstrated that it is possible to use ribosome display as a method exclusively for selection by virtually maintaining the original library repertoire. 

Figure 7.5 A phylogenetic tree of animal phyla based on 18S ribosomal DNA from several laboratories (Raff, 1996). The most significant innovations are the appearance of (1) multicellularity, (2) tissues, (3) the anterior-posterior axis and central nervous system, (5) metameric segmentation, (6) pentameral symmetry, (7) neural crest and amplification of Hox clusters.

The process by which the ribosomes convert the nucleic acid code into the amino acid sequence is appropriately called translation , and the protein synthesis machinery is called the translationa 1 apparatus of the cell. A single mRNA is translated by several ribosomes before it is degraded. Thus a single mRNA molecule gives rise to several molecules of the protein it encodes, causing an amplification of gene expression similar to the situation discussed earlier in the transcription of a gene into several mRNA copies. 

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