Nontranscribed spacer sequences (ITS1 and ITS2) found in the tandemly repeated ribosomal RNA coding units of the nucleolar organizer. Each unit consists of 5′ external transcribed sequence (5′ ETS), 18S rRNA gene, internal transcribed spacer 1 (ITS1), 5.8S rRNA gene, ITS2, 28S rRNA gene, and 3′ ETS. The internal and external spacers are removed and degraded during rRNA maturation. The ITS region is highly conserved intraspecifically, but not interspecifically, and is therefore useful in molecular taxonomy.
Subjects: Medicine and Health.