Critical regions of the pol II rDNA promoter required for pol II
synthesis of rRNA in S. cerevisiae .
Parmeet
Jodhka, Arland Alberts, Matt Haymowicz, Heather Conrad-Webb
Biology, Texas Woman's University, PO Box 425799, Denton, TX 76204,
USA
In Saccharomyces cerevisiae rho0 cells, a
switch occurs in the synthesis of a substantial fraction of cytoplasmic
rRNA from RNA polymerase I (pol I) to RNA polymerase II (pol II) [MCB
15:2420-2428.] In rho0 cells, there is an increase in
episomal copies of rDNA arising from homologous recombination events
within the ribosomal DNA repeat on chromosome XII. From these rDNA
episomes, a cryptic Pol II promoter that overlaps the pol I promoter is
activated to synthesize a functional 35S precursor RNA. Using reporter
genes in which the pol II rDNA promoter is fused to the E.coli LacZ
gene, critical components of the promoter were mapped to a region of
the promoter from -380 to -185. To identify potential regulatory factor
binding sites required for pol II rRNA synthesis, GPS-LS linker scanning
mutagenesis is being conducted. Preliminary analysis of linker insertion
mutations identify a potential negative regulatory element ~300 bp
upstream of the critical region. Linker insertion mutants also confirm
that the region surrounding the transcription initiation site is
required for rDNA transcription by pol II. Further analysis of the
critical sequence elements and regulatory factors required for pol II
synthesis of rRNA is in progress. Supported by NSF grant MCB-9722253 and
NIGMS GM55380.
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