*2.5. Amino Acid Contact Frequency with Nucleotides*

We have also analysed amino acid contacts with each nucleotide in non-ribosomal complexes using 3.5 Å and 6 Å distance cut-offs for contacting residues and the results are shown in Figure 7 and Figure S6. In the 3.5 Å distance criterion, Arg and Lys have a high frequency to bind with nucleotides. Arg and Lys are observed to have the most and least binding frequencies with Guanine and Uracil, respectively. Whereas in the 6 Å criterion, almost the same frequency of binding is observed for Arg and Lys with Adenine, Guanine and Cytosine nucleotides; least binding was observed in the Uracil nucleotide. When compared with the results presented for ordered protein–DNA and protein–RNA complexes in our earlier works, Arg, Lys, Trp, and Tyr were favoured by RNA and Arg was selected by DNA-binding proteins together with Guanine in DNA and Uracil in RNA–protein complexes [36].

**Figure 7.** Normalized amino acid nucleotide contact frequency in non-ribosomal protein–RNA complexes at 3.5 Å.
