The 5' end of yeast 5.8S rRNA is generated by exonucleases from an upstream cleavage site.
We have developed techniques for the detailed analysis of cis-acting sequences in the pre-rRNA of Saccharomyces cerevisiae and used these to study the processing of internal transcribed spacer 1 (ITS1) leading to the synthesis of 5.8S rRNA. As is the case for many eukaryotes, the 5' end of yeast 5.8S rRNA is heterogeneous; we designate the major, short form 5.8S(S), and the minor form (which is seven or eight nucleotides longer) 5.8S(L). These RNAs do not have a precursor/product relationship, but result from the use of alternative processing pathways. In the major pathway, a previously unidentified processing site in ITS1, designated A3, is cleaved. A 10 nucleotide deletion at site A3 strongly inhibits processing of A3 and the synthesis of 5.8S(S); processing is predominantly transferred to the alternative 5.8S(L) pathway. Site A3 lies 76 nucleotides 5' to the end of 5.8S(S), and acts as an entry site for 5'-->3' exonuclease digestion which generates the 5' end of 5.8S(S). This pathway is inhibited in strains mutant for XRN1p and RAT1p. Both of these proteins have been reported to have 5'-->3' exonuclease activity in vitro. Formation of 5.8S(L) is increased by mutations at A3 in cis or in RAT1p and XRN1p in trans, and is kinetically faster than 5.8S(S) synthesis.
Henry
Y
Y
EMBL, Heidelberg, Germany.
Wood
H
H
Morrissey
J P
JP
Petfalski
E
E
Kearsey
S
S
Tollervey
D
D
D001483:Base Sequence; D004252:DNA Mutational Analysis; D004275:DNA, Ribosomal / Q000235:genetics; D005092:Exonucleases / Q000378:metabolism*; D014644:Genetic Variation; D008969:Molecular Sequence Data; D012313:RNA / Q000096:biosynthesis; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012340:RNA, Ribosomal, 5.8S / Q000096:biosynthesis* / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D017384:Sequence Deletion
D004275:DNA, Ribosomal; D012322:RNA Precursors; D012340:RNA, Ribosomal, 5.8S; C039919:RNA, recombinant; D012313:RNA; D005092:Exonucleases