External transcribed spacer

The intergenic spacer includes both non-tran-scribed and external transcribed spacers of... 

Four spacers, the 5 -external transcribed spacer (5 -ETS), the first and second internal transcribed spacers (ITSl and 1TS2), and the 3 -extemal transcribed sequence (3 -ETS), must be removed Removal of the 5 -ETS depends... 

Volkov RA, Komarova NY, Panchuk II, Hemleben V (2003) Molecular evolution of rDNA external transcribed spacer and phylogeny of sect. Petota (genus Solanum). Mol Phylogenet Evol 29 187-202... 

Fig. 1. Schematic representation of eukaryotic rDNA gene. IGR, intergenic region T, terminator ORI, origin of replication spP, spacer promoter pT, promoter-proximal terminator, pP, proximal promoter ETS, external transcribed sequence ITS, internal transcribed sequences.

Eukaryotic rRNAs include 18S (1.8 kb), 5.8S, and 28S (4.7 kb) molecules. They are derived from the nucleolytic processing of a single precursor molecule (pre-rRNA) which is transcribed by RNA polymerase I. The 5.8S RNA remains attached to the 28S RNA by H-bonds. In humans, the pre-rRNA is 13 kb (45S) long and has a structure in which three exons are separated by both internal and external RNA spacers (total length of 31 kb). The fourth component of rRNA is 5S RNA which is transcribed by RNA polymerase III. The 5S rRNA gene is not normally linked to that of other rRNAs. Together with ribosomal proteins, the 18S rRNA constitutes the small 40S ribosomal subunit 5S, 5.8S, and 28S rRNAs make up the large 60S subunit. 

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