The complete nuclear ribosomal DNA (nrDNA) cistron sequence of Pyropia yezoensis (Bangiales, Rhodophyta)

The complete nuclear ribosomal DNA (nrDNA) cistron sequence of Pyropia yezoensis has been sequenced, of which each unit is composed of the intergenic spacer (IGS), the small-subunit (SSU) ribosomal RNA (rRNA) gene, the internal transcribed spacer 1 (ITS1), the 5.8S rRNA gene, the internal transcribed spacer 2 (ITS2), and the large-subunit (LSU) rRNA gene. This cistron occurs in tandem repeats that can number in 100s to 1000s. Furthermore, in the analysis of the sequence data, we determined that introns were present in the small-subunit rRNA genes, for which the exon sequences (1834 bp) are almost identical. The intron numbers ranging from zero to two in the small-subunit rRNA genes are different between multiple individuals. However, the full length of the large-subunit rRNA genes is 4770 bp without any introns, and the 5.8S rRNA gene is 159 bp. Moreover, the 5' and 3' terminal sequences of the genic regions of the ribosomal cistron are extremely conservative even among various species in red alga. In addition, the range for ITS1 is 371-372 bp and for ITS2 is 532 to 535 bp. The IGS is 5984 bp in length and possesses upstream direct repeats, downstream repeats, and middle inverted repeats that make sequencing untoward. This is the first time that the complete nucleotide of the IGS region of P. yezoensis has been sequenced. The provision of the full length of nrDNA cistron will offer useful information to be widely utilized for identification, taxonomic relationships, and phylogenies in red algae.