“…However, there are many other compositional features within the DNA sequences of protein coding genes upon which selection acts. These features include: the genic GC content (4-6) , CpG or TpA dinucleotides (7)(8)(9)(10)(11) , codon pairs (12)(13)(14)(15) , endonuclease recognition sites (16)(17)(18)(19) , intron splicing motifs (20) , mRNA folding stability (21)(22)(23)(24)(25) , ribosomal pausing sites (26,27) , concentration of non-preferred codons at transcripts 5' end (28)(29)(30) , autocorrelation of codons on transcript (31) , and capacity of codon order to influence co-translational folding of proteins (32,33) . At any given site, natural selection may act on one or more of these features to favor the use of certain codons over other synonymous ones (34) .…”