Structures of the domains of human PABPC1. (a) Crystal structure of RRMs 1 and 2 in association with poly(A) . The central two 3 strands of each RRM include two highly conserved sequence motifs, octomeric RNP1 ((K/R)-G-(F/Y)-(G/A)-F-V-X-(F/Y), where X is any amino acid) and hexameric RNP2 ((L/I)-(F/Y)-(V/I)-(G/K)-(N/G)-(L/M)), which is repeated six times. (b) The RNA-binding trough that is present when RRM1 and RRM2 of human associate with poly(A). (c) NMR structure of the five carboxy-terminal helices . Figures were generated by MOLSCRIPT 2.0 using data from Protein data bank (PDB) files (a,b) 1CVJ and (c) 1G9L [125, 126].