The decapping activator Lsm1p-7p–Pat1p complex has the intrinsic ability to distinguish between oligoadenylated and polyadenylated RNAs

Abstract

Decapping is a critical step in mRNA decay. In the 59-to-39 mRNA decay pathway conserved in all eukaryotes, decay is initiated by poly(A) shortening, and oligoadenylated mRNAs (but not polyadenylated mRNAs) are selectively decapped allowing their subsequent degradation by 59 to 39 exonucleolysis. The highly conserved heptameric Lsm1p-7p complex (made up of the seven Sm-like proteins, Lsm1p-Lsm7p) and its interacting partner Pat1p activate decapping by an unknown mechanism and localize with other decapping factors to the P-bodies in the cytoplasm. The Lsm1p-7p-Pat1p complex also protects the 39-ends of mRNAs in vivo from trimming, presumably by binding to the 39-ends. In order to determine the intrinsic RNA-binding properties of this complex, we have purified it from yeast and carried out in vitro analyses. Our studies revealed that it directly binds RNA at/near the 39-end. Importantly, it possesses the intrinsic ability to distinguish between oligoadenylated and polyadenylated RNAs such that the former are bound with much higher affinity than the latter. These results indicate that the intrinsic RNAbinding characteristics of this complex form a critical determinant of its in vivo interactions and functions.

Lsm1-7-Pat1 complex: A link between 3’ and 5’-ends in mRNA decay?

“…Such oligo(A) tail mediated enhancement of RNA binding by this complex was independent of the length or sequence of the body of the RNA. 38 This is consistent with the fact that this complex is needed for the decay of multiple mRNAs in vivo suggesting that it is a general decapping activator for oligoadenylated messages. 32,35,37 Overall these studies suggested that the PAB-mediated inhibition of decapping of polyadenylated mRNAs and the preferential targeting of oligoadenylated mRNAs for decapping by the Lsm1-7-Pat1 complex could together contribute to the deadenylation dependence of decapping in the 5' to 3' mRNA decay pathway.…”

“…Importantly, in vitro analysis of the Lsm1-7-Pat1 complex purified from yeast showed that this complex has the intrinsic ability to distinguish between oligoadenylated and polyadenylated RNAs. 38 These studies revealed an RNA binding property that is unique to this complex which is to bind polyadenylated and unadenylated RNAs with similar affinities but bind oligoadenylated RNAs with several fold higher affinity. Such oligo(A) tail mediated enhancement of RNA binding by this complex was independent of the length or sequence of the body of the RNA.…”

“…39,40 This observation is consistent with the fact that presence of 3'-oligo(A) tail promotes binding of the Lsm1-7-Pat1 complex but inhibits degradation by the cytoplasmic exosome. 12,38 Even normal mRNAs that primarily degrade through the 5' to 3' pathway in vivo degrade via the 3' to 5' pathway when the 5' to 3' pathway is blocked. 14,41 These observations imply that in vivo the efficiency of recruitment of the Lsm1-7-Pat1 complex onto an mRNA could be a key determinant of the major mode of decay (5' to 3' or 3' to 5') of that mRNA.…”

Translation and replication of hepatitis C virus genomic RNA depends on ancient cellular proteins that control mRNA fates

“…This binding then inhibits trimming of the 3Јend while simultaneously promotes decapping and subsequent 5Ј to 3Ј degradation (8,12,21). However, the role of LSm1-7 rings on virus life cycles may be different because viral RNAs have different requirements for their eventual fates.…”

“…Alternatively, these proteins may have a direct and specific effect on the virus and hence directly interact with viral RNA or proteins. In yeast cells, the corresponding proteins Dhh1, Pat1, and the LSm1-7 ring have been shown to interact in vivo (6), and there is evidence of a direct interaction of the LSm1-7 ring with deadenylated cellular mRNAs (8,12). Considering a direct interaction model, it seemed possible that the LSm1-7 ring could interact with the 5Ј and 3ЈUTRs of HCV since they are essential regions in the regulation of viral translation and replication (13), and our translation results suggested a functional link to these sequences.…”