title: Identification and sequence of the initiation site for rat 45S ribosomal RNA synthesis.
abstract: The transcription initiation site for rat 45S precursor ribosomal RNA synthesis was determined by nuclease protection mapping with two single-strand endonucleases. S1 and mung bean, and one single-strand exonuclease, ExoVII. These experiments were performed with end-labeled ribosomal DNA from double-stranded pBR322 recombinants and from single-stranded M13 recombinants. Results from experiments using both kinds of DNA and all three enzymes showed that the 5' end of 45S RNA mapped to a unique site 125 bases upstream from the Hind III site in the ribosomal DNA gene. The DNA surrounding this site (designated +1) was sequenced from -281 to +641. The entire sequence of this region shows extensive homology to the comparable region of mouse. This includes three stretches of T residues in the non-coding strand between +300 and +630. Two sets of direct repeats adjacent to these T-rich regions are observed. Comparison of the mouse and human ribosomal DNA transcription initiation sites with the rat sequence reported in this paper demonstrates a conserved sequence at +2 to +16, CTGACACGCTGTCCT. This suggests that this region may be important for the initiation of transcription on mammalian ribosomal DNAs.
mesh_terms: D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D004262:DNA Restriction Enzymes; D004274:DNA, Recombinant / Q000378:metabolism*; D004275:DNA, Ribosomal; D051379:Mice; D008970:Molecular Weight; D009693:Nucleic Acid Hybridization; D010957:Plasmids; D012335:RNA, Ribosomal / Q000235:genetics*; D051381:Rats; D011919:Rats, Inbred Strains; D013045:Species Specificity; D014158:Transcription, Genetic
chemical_list: D004274:DNA, Recombinant; D004275:DNA, Ribosomal; D012335:RNA, Ribosomal; D004247:DNA; D004262:DNA Restriction Enzymes