U14snoRNAs of the fern, Asplenium nidus, contain large sequence insertions compared with those of higher plants.

Northern analyses of U14snoRNAs in different plant species showed the expected hybridising band of approximately 120 nt in monocotyledonous and dicotyledonous angiosperms. In the lower plant, Bird's nest fern (Asplenium nidus), U14s were larger and three hybridising RNAs of approximately 190, 210 and 250 nt were observed. RT-PCR cloning of all three size variants using primers to the conserved 5' and 3' ends of higher plant U14snoRNAs showed large insertions in one of the plant-specific regions corresponding in position to the yeast U14-specific Y-domain. The insertions are pyrimidine-rich in their 5' halves and purine-rich in their 3' halves and are likely to be sequestered in stem structures consistent with the proposed model of U14snoRNA secondary structure. The 5' flanking regions of one of the fern U14 variants was generated by PCR and lacked classical plant snRNA promoter elements.