The ETS/IGS region in a lower animal, the seawhip, Junceella fragilis (Cnidaria: Anthozoa: Octocorallia): compactness, low variation and apparent conservation of a pre-rRNA processing signal with fungi

Abstract

We determined the nucleotide sequence of an atypically short intergeneic spacer/external transcribed spacer (IGS/ETS) region in the seawhip, Junceella fragilis, and identified an 8-bp motif at the 5'-ETS/18S rDNA boundary closely resembling a fungal pre-rRNA A1 cleavage signal. This apparent conservation of processing signals was unexpected, as no corresponding sequence has previously been reported in any animal. The J. fragilis IGS sequence lacks repetitive motifs of the type typical of higher animals, but a microsatellite is present in the putative 3'-ETS. Comparisons of the IGS between geographically isolated populations of J. fragilis indicate an unexpected lack of sequence variation.