title: Stm1p, a G4 quadruplex and purine motif triplex nucleic acid-binding protein, interacts with ribosomes and subtelomeric Y' DNA in Saccharomyces cerevisiae.
abstract: The Saccharomyces cerevisiae protein Stm1 was originally identified as a G4 quadruplex and purine motif triplex nucleic acid-binding protein. However, more recent studies have suggested a role for Stm1p in processes ranging from antiapoptosis to telomere maintenance. To better understand the biological role of Stm1p and its potential for G(*)G multiplex binding, we used epitope-tagged protein and immunological methods to identify the subcellular localization and protein and nucleic acid partners of Stm1p in vivo. Indirect immunofluorescence microscopy indicated that Stm1p is primarily a cytoplasmic protein, although a small percentage is also present in the nucleus. Conventional immunoprecipitation found that Stm1p is associated with ribosomal proteins and rRNA. This association was verified by rate zonal separation through sucrose gradients, which showed that Stm1p binds exclusively to mature 80 S ribosomes and polysomes. Chromatin immunoprecipitation experiments found that Stm1p preferentially binds telomere-proximal Y' element DNA sequences. Taken together, our data suggest that Stm1p is primarily a ribosome-associated protein, but one that can also interact with DNA, especially subtelomeric sequences. We discuss the implications of our findings in relation to prior genetic, genomic, and proteomic studies that have identified STM1 and/or Stm1p as well as the possible biological role of Stm1p.
authors.affiliation: Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA. mvandyke@mdanderson.org
authors.forename: Michael W
authors.initials: MW
authors.lastname: Van Dyke
authors.forename: Laura D
authors.initials: LD
authors.lastname: Nelson
authors.forename: Rodney G
authors.initials: RG
authors.lastname: Weilbaecher
authors.forename: Dakshesh V
authors.initials: DV
authors.lastname: Mehta
mesh_terms: D020816:Amino Acid Motifs; D015153:Blotting, Western; D002467:Cell Nucleus / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D002843:Chromatin / Q000737:chemistry; D003593:Cytoplasm / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes; D019084:Fluorescent Antibody Technique, Indirect; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D011132:Polyribosomes / Q000737:chemistry; D011233:Precipitin Tests; D011485:Protein Binding; D011687:Purines / Q000737:chemistry; D012335:RNA, Ribosomal / Q000737:chemistry; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry* / Q000378:metabolism*; D016615:Telomere / Q000737:chemistry / Q000648:ultrastructure
chemical_list: D002843:Chromatin; D000939:Epitopes; D008565:Membrane Proteins; D011687:Purines; D012335:RNA, Ribosomal; D029702:Schizosaccharomyces pombe Proteins; C439675:Stm1 protein, S pombe; C030985:purine