|Special features of the second version of the DNA oligonucleotide BarCode for species identification of Hypocrea/Trichoderma|
|ITS1 and 2|
The genes encoding ribosomal RNA (rRNA)are widely used for identifying fungi and for constructing of phylogenetic trees. Ribosomal RNA is needed in a such large amounts to produce the cellular ribosomes that there are multiple codes of the rRNA genes, often arranged in tandem but separated from one another by untranscribed spacers. Each single rRNA gene has coding information for the three types of rRNA found in eukaryotic ribosomes (18S*, 5.8S and 28S), but also contain other valuable information, especially in the internally transcribed spacers (ITS). The rRNA genes initially produce a pre-rRNA, which then undergoes processing, including the excision of the spacer regions, to produce the three ?mature? rRNAs. The 18S rRNA has changed sufficiently over evolutionary time to be used in phylogenetic reconstructions. But the ITS regions are more variable and can often be used to distinguish different fungal species.
* S indicates Svedberg units which reflect the rRNA size detected by the centrifugation in sucrose solution. 28S rRNA is the largest while 5.8S rRNA is the smallest.