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Mol. Cell. Biol., Nov 1995, 6454-6464, Vol 15, No. 11
Z Li, AG Paulovich and JL Woolford Jr
The Saccharomyces cerevisiae CRY1 and CRY2 genes, which encode ribosomal
protein rp59, are expressed at a 10:1 ratio in wild-type cells. Deletion or
inactivation of CRY1 leads to 5- to 10-fold- increased levels of CRY2 mRNA.
Ribosomal protein 59, expressed from either CRY1 or CRY2, represses
expression of CRY2 but not CRY1. cis- Acting elements involved in
repression of CRY2 were identified by assaying the expression of CRY2-lacZ
gene fusions and promoter fusions in CRY1 CRY2 and cry1-delta CRY2 strains.
Sequences necessary and sufficient for regulation lie within the
transcribed region of CRY2, including the 5' exon and the first 62
nucleotides of the intron. Analysis of CRY2 point mutations corroborates
these results and indicates that both the secondary structure and sequence
of the regulatory region of CRY2 pre-mRNA are necessary for repression. The
regulatory sequence of CRY2 is phylogenetically conserved; a very similar
sequence is present in the 5' end of the RP59 gene of the yeast
Kluyveromyces lactis. Wild-type cells contain very low levels of both CRY2
pre-mRNA and CRY2 mRNA. Increased levels of CRY2 pre-mRNA are present in
mtr mutants, defective in mRNA transport, and in upf1 mutants, defective in
degradation of cytoplasmic RNA, suggesting that in wild-type repressed
cells, unspliced CRY2 pre-mRNA is degraded in the cytoplasm. Taken
together, these results suggest that feedback regulation of CRY2 occurs
posttranscriptionally. A model for coupling ribosome assembly and
regulation of ribosomal protein gene expression is proposed.
Copyright © 1995, American Society for Microbiology
Feedback inhibition of the yeast ribosomal protein gene CRY2 is mediated by the nucleotide sequence and secondary structure of CRY2 pre- mRNA
Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
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