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Mol. Cell. Biol., 10 1997, 6175-6183, Vol 17, No. 10
C Cadwell, HJ Yoon, Y Zebarjadian and J Carbon
Yeast Cbf5p was originally isolated as a low-affinity centromeric DNA
binding protein (W. Jiang, K. Middleton, H.-J. Yoon, C. Fouquet, and J.
Carbon, Mol. Cell. Biol. 13:4884-4893, 1993). Cbf5p also binds microtubules
in vitro and interacts genetically with two known centromere-related
protein genes (NDC10/CBF2 and MCK1). However, Cbf5p was found to be
nucleolar and is highly homologous to the rat nucleolar protein NAP57,
which coimmunoprecipitates with Nopp140 and which is postulated to be
involved in nucleolar-cytoplasmic shuttling (U. T. Meier, and G. Blobel, J.
Cell Biol. 127:1505-1514, 1994). The temperature-sensitive cbf5-1 mutant
demonstrates a pronounced defect in rRNA biosynthesis at restrictive
temperatures, while tRNA transcription and pre-rRNA and pre-tRNA cleavage
processing appear normal. The cbf5-1 mutant cells are deficient in
cytoplasmic ribosomal subunits at both permissive and restrictive
temperatures. A high-copy-number yeast genomic library was screened for
genes that suppress the cbf5-1 temperature-sensitive growth phenotype. SYC1
(suppressor of yeast cbf5- 1) was identified as a multicopy suppressor of
cbf5-1 and subsequently was found to be identical to RRN3, an RNA
polymerase I transcription factor. A cbf5delta null mutant is not rescued
by plasmid pNOY103 containing a yeast 35S rRNA gene under the control of a
Pol II promoter, indicating that Cbf5p has one or more essential functions
in addition to its role in rRNA transcription.
Copyright © 1997, American Society for Microbiology
The yeast nucleolar protein Cbf5p is involved in rRNA biosynthesis and interacts genetically with the RNA polymerase I transcription factor RRN3
Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara 93106, USA.
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