The rRNA-processing function of the yeast U14 small nucleolar RNA can be rescued by a conserved RNA helicase-like protein.
The phylogenetically conserved U14 small nucleolar RNA is required for processing of rRNA, and this function involves base pairing with conserved complementary sequences in 18S RNA. With a view to identifying other important U14 interactions, a stem-loop domain required for activity of Saccharomyces cerevisiae U14 RNAs (the Y domain) was first subjected to detailed mutational analysis. The mapping results showed that most nucleotides of the Y domain can be replaced without affecting function, except for loop nucleotides conserved among five different yeast species. Defective variants were then used to identify both intragenic and extragenic suppressor mutations. All of the intragenic mutations mapped within six nucleotides of the primary mutation, suggesting that suppression involves a change in conformation and that the loop element is involved in an essential intermolecular interaction rather than intramolecular base pairing. A high-copy extragenic suppressor gene, designated DBP4 (DEAD box protein 4), encodes an essential, putative RNA helicase of the DEAD-DEXH box family. Suppression by DBP4 (initially CA4 [T.-H. Chang, J. Arenas, and J. Abelson, Proc. Natl. Acad. Sci. USA 87:1571-1575, 1990]) restores the level of 18S rRNA and is specific for the Y domain but is not allele specific. DBP4 is predicted to function either in assembly of the U14 small nucleolar RNP or, more likely, in its interaction with other components of the rRNA processing apparatus. Mediating the interaction of U14 with precursor 18S RNA is an especially attractive possibility.
Liang
W Q
WQ
Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst 01003, USA.
Clark
J A
JA
Fournier
M J
MJ
D000595:Amino Acid Sequence; D001483:Base Sequence; D002466:Cell Nucleolus / Q000378:metabolism*; D053487:DEAD-box RNA Helicases; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D020365:RNA Helicases; D012316:RNA Nucleotidyltransferases / Q000235:genetics*; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000378:metabolism; D012335:RNA, Ribosomal / Q000096:biosynthesis*; D012342:RNA, Small Nuclear / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins
D012331:RNA, Fungal; D012335:RNA, Ribosomal; D012342:RNA, Small Nuclear; D029701:Saccharomyces cerevisiae Proteins; D012316:RNA Nucleotidyltransferases; C106767:HCA4 protein, S cerevisiae; D053487:DEAD-box RNA Helicases; D020365:RNA Helicases