18S rRNA

Aleshin, V.V., Kedrova, O.S., Milyutina, LA, Vladychenskaya, N.S. and Petrov, N.B. (1998) Relationships among nematodes based on the analysis of 18S rRNA gene sequences molecular evidence for a monophyly of chromadorian and secernentean nematodes. Russian Journal of Nematology 6, 175-184. 

Fig. 11.2 The Universal tree based on 16S and 18S rRNA, which is not very different from that generated earlier based on the observable characteristics of organisms.

Eukaryotic ribosomal RNA is transcribed in the nucleolus by RNA polymerase I as a single piece of 45S RNA, which is subsequently deaved to yield 28S rRNA, 18S rRNA, and 5.8S rRNA. RNA polymerase III transcribes the 5S rRNA unit from a separate gene. TTie ribosomal subunits assemble in the nudeolus as the rRNA pieces combine with ribosomal proteins. Eukaryotic ribosomal subunits are 60S and 40S. They join during protein synthesis to form the whole SOS ribosome. 

Tanaka M etal. Isolation of endophytes from plants in Southeast Asia and Japan, and their identiflcation by 18S rRNA gene, Biotechnol Sust Util Biol Res Tropics 13 227-232, 1999. 

The first PCR-based assay for detection of A. niger used sequences from the 18S rRNA gene as the target for primer binding (J imenez etal.,1999). The authors used primers originally published by Melchers et al. (1994),... 

Eukaryotic ribosomes contain four rRNAs analogous to those in prokaryotes the 18S rRNA of the small (40S) subunit and the 28S, 5-8S, and 5S of the large (60S) subunit. 

The start codon is an AUG triplet designating methionine that is distinguished by the Kozak sequence, which base pairs with a portion of the 18S rRNA of the small subunit. 

Fig. 3 Secondary structure of the ribosomal rRNA of Saccharomyces cerevisiae. http //www.ma.icmb.utexas. edu (Cannone et al. 2002). The numbering of nucleotides is according to E. coli. Helices H) discussed in the text are highlighted and localization of yeast rdn mutations are indicated, a Secondary structure of the small subunit 18S rRNA. Helices discussed in the text are labeled in red. b Secondary structure of the 25 rRNA. Helices discussed in the text are labeled in blue. Helix 44 is part of the L7/L12 stalk hehx 95 contains the sarcin-ricin loop. For details, see text...

Velichutina IV, Dresios J, Hong JY, Li C, Mankin A, Synetos D, Liebman SW (2000) Mutations in helix 27 of the yeast Saccharomyces cerevisiae 18S rRNA affect the function of the decoding center of the ribosome. RNA 6 1174-1184... 

Figure 28-17 (A) Electron micrograph of the 45S precursor of rRNA from HeLa cells after spreading from 80% formamide and 4 M urea. The molecule is shown in reverse contrast. (B) Tracing of molecule in (A) showing several regions of secondary structure as hairpin loops. The 28S and 18S rRNA regions are indicated. (C) 32S rRNA. (D) 28S rRNA. Notice that the same secondary structure can be seen in the 28S RNA as in its 32S and 45S precursors. From Wellauer and Dawid.527...

Table 4.2. Numbers of nSSU and nLSU sequences for neodermatans found on 28 February 2005 by submitting a series of queries to GenBank modelled on this example 18S rRNA gene AND Trematoda[Orgn] .This recovers all relevant accessions including partial sequences and multiple accessions for the same species.

A prokaryotic 70S ribosome comprises two subunits (50S and 30S). The 50S subunit has 23S and 5S rRNAs complexed with 34 polypeptides whereas the 30S subunit contains 16S rRNA and 21 polypeptides. A eukaryotic 80S ribosome comprises two subunits (60S and 40S). The 50S subunit has 28S, 5.8S and 5S rRNAs complexed with approx. 49 polypeptides whereas the 40S subunit contains 18S rRNA and about 33 polypeptides. 

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