PMID: 21098120

Authors:

Yang R, Gaidamakov SA, Xie J, Lee J, Martino L, Kozlov G, Crawford AK, Russo AN, Conte MR, Gehring K, Maraia RJ

Title:

LARP4 binds poly(A), interacts with poly(A)-binding protein MLLE domain via a variant PAM2w motif and can promote mRNA stability.

Journal:

Mol Cell Biol. 2010 Nov 22.

Abstract:

The conserved RNA binding protein La recognizes UUU-3'OH on its small nuclear RNA ligands and stabilizes them from 3' end-mediated decay. We report that La-related protein-4 (LARP4) is a newly described factor that can bind poly(A) RNA and interact with poly(A) binding protein (PABP). Yeast two-hybrid analysis and reciprocal IPs from HeLa cells reveal that LARP4 interacts with RACK1, a 40S ribosome- and mRNA-associated protein. LARP4 cosediments with 40S ribosome subunits and polyribosomes, and its knockdown decreases translation. Mutagenesis of the RNA binding or PABP interaction motifs decrease LARP4 association with polysomes. Several translation and mRNA metabolism-related proteins use a PAM2 sequence containing a critical invariant phenylalanine to make direct contact with the MLLE domain of PABP, and their competition for the MLLE is thought to regulate mRNA homeostasis. Unlike all approximately 150 previously analyzed PAM2 sequences, LARP4 contains a variant PAM2 with tryptophan (PAM2w) in place of the phenylalanine. Binding and NMR studies show that a peptide representing LARP4 PAM2w interacts with the MLLE of PABP within the affinity range measured for other PAM2 motif peptides. A cocrystal of PABC bound to LARP4 PAM2w shows tryptophan in the pocket in PABC-MLLE otherwise occupied by phenylalanine. We present evidence that LARP4 expression stimulates luciferase reporter activity by promoting mRNA stability, as shown by mRNA decay analysis of luciferase and cellular mRNAs. We propose that LARP4 activity is integrated with other PAM2-protein activities by PABP as part of mRNA homeostasis.