RSCU

Many amino acids are coded by more than one codon A codon is triplet of nucleotides that codes for a specific amino acid.RH_Codon; thus multiple codons for a given amino acid are synonymousRH_Synonymous_change.  However, many genes display a non-random usage of synonymous codons for specific amino acids.  A measure of the extent of this non-randomness is given by the Relative Synonymous Codon Usage (RSCU) (Sharp et al. 1986Sharp_et_al_1986).

The RSCU for a particular codon (i) is given by                            

            RSCUi  =  Xi / åå XI /n

where Xi is the number of times the ith codon has been used for a given amino acid, and n is the number of synonymous codons for that amino acid.