LSm1-7 complexes bind to specific sites in viral RNA genomes and regulate their translation and replication

Abstract

LSm1-7 complexes promote cellular mRNA degradation, in addition to translation and replication of positive-strand RNA viruses such as the Brome mosaic virus (BMV). Yet, how LSm1-7 complexes act on their targets remains elusive. Here, we report that reconstituted recombinant LSm1-7 complexes directly bind to two distinct RNA-target sequences in the BMV genome, a tRNA-like structure at the 39-untranslated region and two internal A-rich single-stranded regions. Importantly, in vivo analysis shows that these sequences regulate the translation and replication of the BMV genome. Furthermore, both RNA-target sequences resemble those found for Hfq, the LSm counterpart in bacteria, suggesting conservation through evolution. Our results provide the first evidence that LSm1-7 complexes interact directly with viral RNA genomes and open new perspectives in the understanding of LSm1-7 functions.

The Lsm1-7-Pat1 complex promotes viral RNA translation and replication by differential mechanisms

“…Two separate plasmids that express BMV RNA3 and an allele (mutant or WT) of LSM1, respectively, were introduced into the lsm1Δ strain with or without an additional third plasmid expressing the 1a protein. In the absence of protein 1a, RNA3 accumulates to similar levels in all lsm1 mutants assayed (data not shown) indicating that, as previously shown (Mas et al 2006;Galao et al 2010), Lsm1 does not affect BMV RNA3 steady state. When 1a was coexpressed, the recruitment of RNA3 was inhibited in lsm1Δ cells as evident from the poor accumulation of RNA3 in those cells compared with the WT cells ( Fig.…”

“…7C). These results show that the yeast complex is similar to the human complex with regard to its relative binding affinities for the different regions of the BMV RNAs (Galao et al 2010).…”

“…(Galao et al 2010). Yet, how Lsm1-7-Pat1 facilitates both translation and recruitment of viral genomes remains unclear.…”

The C-terminal extension of Lsm4 interacts directly with the 3′ end of the histone mRNP and is required for efficient histone mRNA degradation

“…The mechanism by which Lsm1-7 is recruited to any RNA substrate is not well understood. Lsm1-7 has a higher affinity for oligo(A) or oligo(U) RNA at the 3 ′ end of mRNAs (Chowdhury et al 2007;Chowdhury and Tharun 2008), and the complex can also bind to oligo(A) stretches at the 5 ′ end of orthopox viral mRNAs (Bergman et al 2007), as well as internal oligo(A) sites in other viral mRNAs (Galao et al 2010). Protein-protein interactions, such as those shown here with SLBP and 3 ′ hExo, may provide additional specificity that allows for association of the Lsm1-7 complex preferentially with RNAs being targeted for degradation.…”

The Lsm Proteins: Ring Architectures for RNA Capture

“…A role for Lsm1 as an effector of HIV replication has been reported (Chable-Bessia et al, 2009). It has also been suggested more recently that positive-strand RNA viruses may directly bind to the host Lsm1-7 protein complex via tRNA-like structures and A-rich stretches, so diverting normal mRNA regulation (Galao et al, 2010). The requirement of host Lsm proteins for the replication of this class of virus has additionally been demonstrated in plant brome mosaic virus (Diez et al, 2000;Noueiry et al, 2003;Mas et al, 2006) and human hepatitis C virus (Scheller et al, 2009).…”