Relative Synonymous Codon Usage

Relative Synonymous Codon Usage (RSCU) is a simple measure of non-uniform usage of synonymous codons in a coding sequence. RSCU values are the number of times a particular codon is observed, relative to the number of times that the codon would be observed for a uniform synonymous codon usage (i.e. all the codons for a given amino-acid have the same probability). In the absence of any codon usage bias, the RSCU values would be 1.00 (this is the case for sequence CDs in the example thereafter). A codon that is used less frequently than expected will have an RSCU value of less than 1.00 and vice versa for a codon that is used more frequently than expected.