doi:10.1093/nar/gkn102 Dissecting protein–RNA recognition sites

We analyze the protein–RNA interfaces in 81 tran-sient binary complexes taken from the Protein Data Bank. Those with tRNA or duplex RNA are larger than with single-stranded RNA, and comparable in size to protein–DNA interfaces. The protein side bears a strong positive electrostatic potential and resem-bles protein–DNA interfaces in its amino acid com-position. On theRNAside, the phosphate contributes less, and the sugar much more, to the interaction than in protein–DNA complexes. On average, protein–RNA interfaces contain 20 hydrogen bonds, 7 that involve the phosphates, 5 the sugar 2’OH, and 6 the bases, and 32 water molecules. The average H-bond density per unit buried surface area is less with tRNA or single-stranded RNA than with duplex RNA. The atomic packing is also less compact in inter-faces with tRNA. On the protein side, the main chain NH and Arg/Lys side chains account for nearly half of all H-bonds toRNA; themain chain COand side chain acceptor groups, for a quarter. The 2’OH is a major player in protein–RNA recognition, and shape com-plementarity an important determinant, whereas electrostatics and direct base–protein interactions play a lesser part than in protein–DNA recognition