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Mol. Cell. Biol., 07 1997, 4124-4132, Vol 17, No. 7
WQ Liang, JA Clark and MJ Fournier
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.
Copyright © 1997, American Society for Microbiology
The rRNA-processing function of the yeast U14 small nucleolar RNA can be rescued by a conserved RNA helicase-like protein
Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst 01003, USA.
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