Recognition signals for mouse pre-rRNA processing. A potential role for U3 nucleolar RNA.

In order to identify signals for rRNA processing in eukaryotes, mouse pre-rRNA sequence features around four cleavage sites have been analyzed. No consensus sequence can be recognized when the four boundary regions are examined. Unlike mature rRNA termini, distal sequences of precursor-specific domains cannot participate in stable duplex with adjacent regions. The extensive divergence of precursor-specific sequences during evolution also applies to nucleotides adjacent to cleavage sites, with a significant exception for a conserved segment immediately downstream 5.8S rRNA. A specific role is proposed for U3 nucleolar RNA in the conversion of 32S pre-rRNA into mature 28S rRNA, through base-pairing with precursor-specific sequences at the boundaries of excised domains.