(A) PTM status can alter sub-cellular localization. ELAVL1 is a multi-functional nucleocytoplasmic shuttling RBP whose methylation results in its export from the nucleus, where it participates in splicing, to the cytoplasm where it regulates mRNAs containing AREs in their 5′- or 3′-UTR (i–iii). It is unclear which enzyme removes this PTM (represented by ‘?’) facilitating its nuclear import. (B) PTM at one residue can affect another. eIF5A is hypusinated at Lys⁵⁰ enabling its export to the cytoplasm where it functions in mRNA translation/stability (i and ii). However, Lys⁴⁷ acetylation by P300/CBP-associated factor (PCAF) antagonizes h retaining eIF5A in the nucleus. Acetylation may be reversed by HDAC6/Sirtuin (SIRT2) (C) Protein–protein and (D) RNA–protein interactions are PTM sensitive. (C) Non-methylated FMRP binds paralogues FXR1P and FXR2P inefficiently. Methylation by PRMT4 enhances FMRP heterodimerization with FXR1P and FXR2P, but has no apparent effect on FMRP homodimerization, thus regulating the composition of mRNP complexes. (D) PRMT4-directed FMRP methylation at Arg^533/538 or Arg^543/545 blocks binding to specific mRNA subsets (ORF 1) but binding to other mRNA targets (ORF2) is unaffected. Red and green arrows, nuclear export and import respectively; wavy lines mRNA. Blue arrows represent interactions, with broader blue arrows representing enhanced interactions and dotted blue lines with a cross representing impeded interactions.