La Ribonucleoprotein Domain Family, Member 4 (LARP4)

LARP4 can bind poly(A) RNA and interact with poly(A) binding protein (PABP). 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. LARP4 contains a variant PAM2 with tryptophan (PAM2w) in place of the phenylalanine. A cocrystal of PABC bound to LARP4 PAM2w shows tryptophan in the pocket in PABC-MLLE otherwise occupied by phenylalanine. LARP4 expression stimulates luciferase reporter activity by promoting mRNA stability, as shown by mRNA decay analysis of luciferase and cellular mRNAs. LARP4 activity is integrated with other PAM2-protein activities by PABP as part of mRNA homeostasis.