title: Both Sm-domain and C-terminal extension of Lsm1 are important for the RNA-binding activity of the Lsm1-7-Pat1 complex.
abstract: Lsm proteins are a ubiquitous family of proteins characterized by the Sm-domain. They exist as hexa- or heptameric RNA-binding complexes and carry out RNA-related functions. The Sm-domain is thought to be sufficient for the RNA-binding activity of these proteins. The highly conserved eukaryotic Lsm1 through Lsm7 proteins are part of the cytoplasmic Lsm1-7-Pat1 complex, which is an activator of decapping in the conserved 5'-3' mRNA decay pathway. This complex also protects mRNA 3'-ends from trimming in vivo. Purified Lsm1-7-Pat1 complex is able to bind RNA in vitro and exhibits a unique binding preference for oligoadenylated RNA (over polyadenylated and unadenylated RNA). Lsm1 is a key subunit that determines the RNA-binding properties of this complex. The normal RNA-binding activity of this complex is crucial for mRNA decay and 3'-end protection in vivo and requires the intact Sm-domain of Lsm1. Here, we show that though necessary, the Sm-domain of Lsm1 is not sufficient for the normal RNA-binding ability of the Lsm1-7-Pat1 complex. Deletion of the C-terminal domain (CTD) of Lsm1 (while keeping the Sm-domain intact) impairs mRNA decay in vivo and results in Lsm1-7-Pat1 complexes that are severely impaired in RNA binding in vitro. Interestingly, the mRNA decay and 3'-end protection defects of such CTD-truncated lsm1 mutants could be suppressed in trans by overexpression of the CTD polypeptide. Thus, unlike most Sm-like proteins, Lsm1 uniquely requires both its Sm-domain and CTD for its normal RNA-binding function.
authors.affiliation: Department of Biochemistry, Uniformed Services University of the Health Sciences (USUHS), Bethesda, Maryland 20814-4799, USA.
authors.forename: Ashis
authors.initials: A
authors.lastname: Chowdhury
authors.forename: Kalidindi K
authors.initials: KK
authors.lastname: Raju
authors.forename: Swathi
authors.initials: S
authors.lastname: Kalurupalle
authors.forename: Sundaresan
authors.initials: S
authors.lastname: Tharun
mesh_terms: D046912:Multiprotein Complexes / Q000378:metabolism*; D054730:Protein Interaction Domains and Motifs; D012313:RNA / Q000378:metabolism*; D039381:RNA Cap-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: C114069:LSM1 protein, S cerevisiae; C521832:LSM7 protein, S cerevisiae; D046912:Multiprotein Complexes; C103266:PAT1 protein, S cerevisiae; D039381:RNA Cap-Binding Proteins; D016601:RNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D012313:RNA