title: Mapping of the major early endonuclease cleavage site of the rat precursor to rRNA within the internal transcribed spacer sequence of rDNA.
abstract: The endonuclease cleavage of 41 S pre-rRNA to yield 32 S and 21 S pre-rRNA constitutes a major early step in the processing of pre-rRNA in rat liver. The 5'-terminus of 32 S pre-rRNA and the 3'-terminus of 21 S pre-rRNA were precisely located within the rDNA sequence by S1 nuclease protection mapping and use of appropriate rDNA restriction fragments. The 5'-terminus of 12 S pre-rRNA, an initial product of 32 S pre-rRNA processing, was also mapped within the rDNA sequence. The 5'-termini of 32 S and 12 S pre-rRNA coincide and map within a 14-residue T-tract (non-coding strand) at 161-163 bp upstream from the 5'-end of the 5.8 S rRNA gene. The 3'-terminus of 21 S pre-rRNA maps within the same T-tract. These results show that the endonuclease cleavage occurs within a U-tract in the internal transcribed spacer 1 sequence of 41 S pre-rRNA. The homogeneity of the 5'- or 3'-termini of 32 S, 12 S and 21 S pre-rRNA indicates also that the terminal processing of these molecules, if any, is markedly slower. The coincidence in the location of 32 S and 12 S pre-rRNA 5'-termini shows further that the endonuclease cleavage of 32 S pre-rRNA precedes the removal of its 5'-terminal segment to yield 5.8 S rRNA. The absence in the whole pre-rRNA internal transcribed spacer of sequences complementary to the target U-tract suggests that the endonuclease cleavage, generating 32 S and 21 S pre-rRNA, occurs in a single-stranded loop of U-residues.
mesh_terms: D001483:Base Sequence; D002466:Cell Nucleolus / Q000378:metabolism; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics*; D004275:DNA, Ribosomal; D004720:Endonucleases; D004722:Endoribonucleases / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008970:Molecular Weight; D009690:Nucleic Acid Conformation; D009694:Nucleic Acid Precursors / Q000235:genetics* / Q000302:isolation & purification; D012322:RNA Precursors; D012335:RNA, Ribosomal / Q000235:genetics* / Q000302:isolation & purification; D015719:Single-Strand Specific DNA and RNA Endonucleases; D014158:Transcription, Genetic
chemical_list: D004275:DNA, Ribosomal; D009694:Nucleic Acid Precursors; D012322:RNA Precursors; D012335:RNA, Ribosomal; D004247:DNA; D004720:Endonucleases; D004722:Endoribonucleases; C041816:pre-ribosomal RNA endoribonuclease; D015719:Single-Strand Specific DNA and RNA Endonucleases