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Two distinct recognition signals define the site of endonucleolytic cleavage at the 5′‐end of yeast 18S rRNA.
Author(s) -
Venema J.,
Henry Y.,
Tollervey D.
Publication year - 1995
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1995.tb00169.x
Subject(s) - biology , cleavage (geology) , 18s ribosomal rna , yeast , ribosomal rna , genetics , computational biology , microbiology and biotechnology , gene , paleontology , fracture (geology)
Three of the four eukaryotic ribosomal RNA molecules (18S, 5.8S and 25–28S rRNA) are transcribed as a single precursor, which is subsequently processed into the mature species by a complex series of cleavage and modification reactions. Early cleavage at site A1 generates the mature 5′‐end of 18S rRNA. Mutational analyses have identified a number of upstream regions in the 5′ external transcribed spacer (5′ ETS), including a U3 binding site, which are required in cis for processing at A1. Nothing is known, however, about the requirement for cis‐acting elements which define the position of the 5′‐end of the 18S rRNA or of any other eukaryotic rRNA. We have introduced mutations around A1 and analyzed them in vivo in a genetic background where the mutant pre‐rRNA is the only species synthesized. The results indicate that the mature 5′‐end of 18S rRNA in yeast is identified by two partially independent recognition systems, both defining the same cleavage site. One mechanism identifies the site of cleavage at A1 in a sequence‐specific manner involving recognition of phylogenetically conserved nucleotides immediately upstream of A1 in the 5′ ETS. The second mechanism specifies the 5′‐end of 18S rRNA by spacing the A1 cleavage at a fixed distance of 3 nt from the 5′ stem‐loop/pseudoknot structure located within the mature sequence. The 5′ product of the A1 processing reaction can also be identified, showing that, in contrast to yeast 5.8S rRNA, the 5′‐end of 18S rRNA is generated by endonucleolytic cleavage.