title: Atomic model of human Rcd-1 reveals an armadillo-like-repeat protein with in vitro nucleic acid binding properties.
abstract: Rcd-1, a protein highly conserved across eukaryotes, was initially identified as a factor essential for nitrogen starvation-invoked differentiation in fission yeast, and its Saccharomyces cerevisiae homolog, CAF40, has been identified as part of the CCR4-NOT transcription complex, where it interacts with the NOT1 protein. Mammalian homologs are involved in various cellular differentiation processes including retinoic acid-induced differentiation and hematopoetic cell development. Here, we present the 2.2 A X-ray structure of the highly conserved region of human Rcd-1 and investigate possible functional abilities of this and the full-length protein. The monomer is made up of six armadillo repeats forming a solvent-accessible, positively-charged cleft 21-22 A wide that, in contrast to other armadillo proteins, stays fully exposed in the dimer. Prompted by this finding, we established that Rcd-1 can bind to single- and double-stranded oligonucleotides in vitro with the affinity of G/C/T >> A. Mutation of an arginine residue within the cleft strongly reduced or abolished oligonucleotide binding. Rcd-1's ability to bind to nucleic acids, in addition to the previously reported protein-protein interaction with NOT1, suggests a new feature in Rcd-1's role in regulation of overall cellular differentiation processes.
authors.affiliation: Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Garces
authors.forename: Wanda
authors.initials: W
authors.lastname: Gillon
authors.forename: Emil F
authors.initials: EF
authors.lastname: Pai
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002850:Chromatography, Gel; D002942:Circular Dichroism; D018360:Crystallography, X-Ray / Q000379:methods; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009696:Nucleic Acids / Q000378:metabolism*; D011485:Protein Binding; D016415:Sequence Alignment; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: C468527:CNOT9 protein, human; D009696:Nucleic Acids; D014157:Transcription Factors