Sequence and secondary structure of mouse 28S rRNA 5'terminal domain. Organisation of the 5.8S-28S rRNA complex

We present the sequence of the 5' terminal 585 nucleotides of mouse 28S rRNA as inferred from the DNA sequence of a cloned gene fragment. The comparison of mouse 28S rRNA sequence with its yeast homolog, the only known complete sequence of eukaryotic nucleus-encoded large rRNA (see ref. 1, 2) reveals the strong conservation of two large stretches which are interspersed with completely divergent sequences. These two blocks of homology span the two segments which have been recently proposed to participate directly in the 5.8S-large rRNA complex in yeast (see ref. 1) through base-pairing with both termini of 5.8S rRNA. The validity of the proposed structural model for 5.8S-28S rRNA complex in eukaryotes is strongly supported by comparative analysis of mouse and yeast sequences: despite a number of mutations in 28S and 5.8S rRNA sequences in interacting regions, the secondary structure that can be proposed for mouse complex is perfectly identical with yeast's, with all the 41 base-pairings between the two molecules maintained through 11 pairs of compensatory base changes. The other regions of the mouse 28S rRNA 5'terminal domain, which have extensively diverged in primary sequence, can nevertheless be folded in a secondary structure pattern highly reminiscent of their yeast' homolog. A minor revision is proposed for mouse 5.8S rRNA sequence.