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Molecular and Cellular Biology, November 2000, p. 8124-8133, Vol. 20, No. 21
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Multiple Mechanisms of Suppression Circumvent Transcription Defects in an RNA Polymerase Mutant

Qian Tan, Xin Li,dagger Parag P. Sadhale,Dagger Takenori Miyao, and Nancy A. Woychik*

Department of Molecular Genetics and Microbiology, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854

Received 3 May 2000/Returned for modification 12 June 2000/Accepted 9 August 2000

Using a high-copy-number suppressor screen to obtain clues about the role of the yeast RNA polymerase II subunit RPB4 in transcription, we identified three suppressors of the temperature sensitivity resulting from deletion of the RPB4 gene (Delta RPB4). One suppressor is Sro9p, a protein related to La protein, another is the nucleosporin Nsp1p, and the third is the RNA polymerase II subunit RPB7. Suppression by RPB7 was anticipated since its interaction with RPB4 is well established both in vitro and in vivo. We examined the effect of overexpression of each suppressor gene on transcription. Interestingly, suppression of the temperature-sensitive phenotype correlates with the correction of a characteristic transcription defect of this mutant: each suppressor restored the level of promoter-specific, basal transcription to wild-type levels. Examination of the effects of the suppressors on other in vivo transcription aberrations in Delta RPB4 cells revealed significant amelioration of defects in certain inducible genes in Sro9p and RPB7, but not in Nsp1p, suppressor cells. Analysis of mRNA levels demonstrated that overexpression of each of the three suppressors minimally doubled the mRNA levels during stationary phase. However, the elevated mRNA levels in Sro9p suppressor cells appear to result from a combination of enhanced transcription and message stability. Taken together, these results demonstrate that these three proteins influence transcription and implicate Sro9p in both transcription and posttranscription events.

* Corresponding author. Mailing address: University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Department of Molecular Genetics and Microbiology, 675 Hoes La., Piscataway, NJ 08854-5635. Phone: (732) 235-4534. Fax: (732) 235-5037. E-mail: woychina{at}umdnj.edu.

dagger Present address: Schering-Plough Research Institute, Kenilworth, NJ 07033-0539.

Dagger Present address: Indian Institute of Science, Department of Microbiology and Cell Biology, Bangalore, India.

Molecular and Cellular Biology, November 2000, p. 8124-8133, Vol. 20, No. 21
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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