Fig. 3

Tests of protein molecular evolution of eutherian fibroblast growth factors. a Relative synonymous codon usage statistics of eutherian FGF gene data set. The not preferable amino acid codons were indicated by white letters on red backgrounds. Counts, observed amino acid codon counts; R, relative synonymous codon usage statistics; &, stop codons. b Reference human FGF1A protein amino acid sequence. The 19 invariant amino acid sites were shown using white letters on violet backgrounds. Whereas the 5 amino acid sites that were invariant among 22 FGF major protein clusters were indicated by black arrows (except that M1 was invariant among 266 FGF protein primary structures), grey arrows indicated 2 amino acid sites that were invariant among 21 FGF major protein clusters respectively. The 3 forward amino acid sites were shown using white letters on red backgrounds. The stars labelled 2 forward amino acid sites described among 22 FGF major protein clusters. The positions of 12 β-strands implicated in β-trefoil protein tertiary structure were indicated below reference human FGF1A protein primary structure [22, 24]