title: Structure-function analysis and genetic interactions of the SmG, SmE, and SmF subunits of the yeast Sm protein ring.
abstract: A seven-subunit Sm protein ring forms a core scaffold of the U1, U2, U4, and U5 snRNPs that direct pre-mRNA splicing. Using human snRNP structures to guide mutagenesis in Saccharomyces cerevisiae, we gained new insights into structure-function relationships of the SmG, SmE, and SmF subunits. An alanine scan of 19 conserved amino acids of these three proteins, comprising the Sm RNA binding sites or inter-subunit interfaces, revealed that, with the exception of Arg74 in SmF, none are essential for yeast growth. Yet, for SmG, SmE, and SmF, as for many components of the yeast spliceosome, the effects of perturbing protein-RNA and protein-protein interactions are masked by built-in functional redundancies of the splicing machine. For example, tests for genetic interactions with non-Sm splicing factors showed that many benign mutations of SmG, SmE, and SmF (and of SmB and SmD3) were synthetically lethal with null alleles of U2 snRNP subunits Lea1 and Msl1. Tests of pairwise combinations of SmG, SmE, SmF, SmB, and SmD3 alleles highlighted the inherent redundancies within the Sm ring, whereby simultaneous mutations of the RNA binding sites of any two of the Sm subunits are lethal. Our results suggest that six intact RNA binding sites in the Sm ring suffice for function but five sites may not.
authors.affiliation: Microbiology and Immunology Department, Weill Cornell Medical College, New York, New York 10065, USA.
authors.forename: Beate
authors.initials: B
authors.lastname: Schwer
authors.affiliation: Microbiology and Immunology Department, Weill Cornell Medical College, New York, New York 10065, USA.
authors.forename: Joshua
authors.initials: J
authors.lastname: Kruchten
authors.affiliation: Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10065, USA.
authors.forename: Stewart
authors.initials: S
authors.lastname: Shuman
mesh_terms: D001665:Binding Sites; D009154:Mutation; D011485:Protein Binding; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000072260:RNA Splicing Factors / Q000235:genetics / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017381:Spliceosomes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D021122:Protein Subunits; D000072260:RNA Splicing Factors; D017411:Ribonucleoproteins, Small Nuclear; D029701:Saccharomyces cerevisiae Proteins
keywords: Sm ring subunits; pre-mRNA splicing; snRNPs