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Published November 1990 | Published
Journal Article Open

SSB-1 of the yeast Saccharomyces cerevisiae is a nucleolar-specific, silver-binding protein that is associated with the snR10 and snR11 small nuclear RNAs


SSB-1, the yeast single-strand RNA-binding protein, is demonstrated to be a yeast nucleolar-specific, silver-binding protein. In double-label immunofluorescence microscopy experiments antibodies to two other nucleolar proteins, RNA Pol I 190-kD and fibrillarin, were used to reveal the site of rRNA transcription; i.e., the fibrillar region of the nucleolus. SSB-1 colocalized with fibrillarin in a double-label immunofluorescence mapping experiment to the yeast nucleolus. SSB-1 is located, though, over a wider region of the nucleolus than the transcription site marker. Immunoprecipitations of yeast cell extracts with the SSB-1 antibody reveal that in 150 mM NaCl SSB-1 is bound to two small nuclear RNAs (snRNAs). These yeast snRNAs are snR10 and snR11, with snR10 being predominant. Since snR10 has been implicated in pre-rRNA processing, the association of SSB-1 and snR10 into a nucleolar snRNP particle indicates SSB-1 involvement in rRNA processing as well. Also, another yeast protein, SSB-36-kD, isolated by single- strand DNA chromatography, is shown to bind silver under the conditions used for nucleolar-specific staining. It is, most likely, another yeast nucleolar protein.

Additional Information

© 1990 by The Rockefeller University Press. Received for publication 27 March 1990 and in revised form 27 July 1990. We thank A. Sentenac at Service de Biochimie, Gif-sur-Yvette, Cedex, France and E. Tan at Scripps Clinic, La Jolla, Ca, for the antisera to RNA Pol I 190-kD protein and fibrillarin (mouse monoclonal), respectively. We thank A. Jong at the University of Southern California, Los Angeles, CA, and M. Cusick at Texas A&M University, College Station, TX, for the purified SSB-1 protein and ssDNA cellulose column fractions. We thank E. Shuster at the University of California, San Francisco, CA for the clones of the yeast snRNAs and E. Jones at Carnegie-Mellon University, Pittsburgh, PA, for yeast strain EJ101. M.W. Clark was supported by the National Institutes of Health (NIH) postdoctoral fellowship 5F32 GM 1008-02. M.L.R. Yip was supported by Howard Hughes Institute Doctoral Fellowship in Biological Sciences. J. Campbell was supported by NIH grant GM 25588. J. Abelson was supported by NIH grant GM 3267.

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