Extreme variations in the ratios of non-synonymous to synonymous nucleotide substitution rates in signal peptide evolution.
Nucleotide sequences encoding signal peptides from the precursors of alpha-amylase/trypsin inhibitors from cereals are homologous to those corresponding to the precursors of thaumatin II and of plastocyanins. Non-synonymous (KA) and synonymous (KS) rates of nucleotide substitutions have been calculated for all possible binary combinations. Extreme variation in KA/KS ratios has been observed; from the 0.167 average found within the plastocyanin family to an average of 1.90 calculated for the inhibitors/thaumatin II transition. A similar calculation has been carried out for the signal peptide sequences of thionins, which are unrelated to those of the alpha-amylase/trypsin inhibitor family, and an average KA/KS of 0.12 has been obtained. This variation can be largely explained in terms of an empirical index of stability related to amino acid composition and seems to be independent of functional constraints.
Garcia-Maroto
F
F
Bioquímica y Biología Molecular, E.T.S. Ingenieros Agrónomos-UPM, Madrid, Spain.
Castagnaro
A
A
Sanchez de la Hoz
P
P
Maraña
C
C
Carbonero
P
P
García-Olmedo
F
F
D000595:Amino Acid Sequence; D000681:Amylases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics; D001483:Base Sequence; D005075:Biological Evolution; D001467:Hordeum / Q000032:analysis / Q000235:genetics; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics; D010944:Plants / Q000032:analysis / Q000235:genetics*; D010970:Plastocyanin / Q000737:chemistry / Q000235:genetics; D011498:Protein Precursors / Q000737:chemistry / Q000235:genetics*; D021382:Protein Sorting Signals / Q000737:chemistry / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D013549:Sweetening Agents; D014908:Triticum / Q000032:analysis / Q000235:genetics; D014361:Trypsin Inhibitors / Q000737:chemistry / Q000235:genetics*; D000516:alpha-Amylases / Q000037:antagonists & inhibitors
D010940:Plant Proteins; D011498:Protein Precursors; D021382:Protein Sorting Signals; D013549:Sweetening Agents; D014361:Trypsin Inhibitors; C057542:thaumatin II protein, Thaumatococcus daniellii; D010970:Plastocyanin; D000681:Amylases; D000516:alpha-Amylases