RSCU

Introduction

It is used to describe the relative usage of each codon in species (or part of species).

Its value ranges from 0 to 6.

Methionine, tryptophan, and stop codons are usually omitted.

How to calculate?

\[\operatorname{RSCU}_{i j}=\frac{x_{i j}}{\frac{1}{n_{i}} \sum_{j=1}^{n_{i}} x_{i j}}\]

\(x_{i j}\) is the number of occurrences of the jth codon for the ith amino acid.

\({\frac{1}{n_{i}} \sum_{j=1}^{n_{i}} x_{i j}}\) is the average codon use of a codon family.

Meaning of value

• 0 refers to the absence of this codon.
• 1 refer to this codon is no bias.
• 6 refers to this codon as the only codon used in a six-codon family.​

1. Codon usage in yeast: cluster analysis clearly differentiates highly and lowly expressed genes: page 3
2. Synonymous but not the same: the causes and consequences of codon bias: page 2

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