A study of the ITS1 nucleotide sequences of 1000 moss species of 62 families, 11 liverwort species from five orders, and one hornwort Anthoceros agrestis identified five highly conserved motifs (CM1-CM5), which are presumably involved in pre-rRNA processing. Although the ITS1 sequences substantially differ in length and the extent of divergence, the conserved motifs are found in all of them. ITS1 secondary structures were constructed for 76 mosses, and main regularities at conserved motif positioning were observed. The positions of processing sites in the ITS1 secondary structure of the yeast Saccharomyces cerevisiae were found to be similar to the positions of the conserved motifs in the ITS1 secondary structures of mosses and liverworts. In addition, a potential hairpin formation in the putative secondary structure of a pre-rRNA fragment was considered for the region between ITS1 CM4-CM5 and a highly conserved region between hairpins 49 and 50 (H49 and H50) of the 18S rRNA.
Keywords: ITS1; conserved motifs; mosses; processing; secondary structure.