Coding Sequence
CDSAlso known as: open reading frame, ORF
The portion of a gene or mRNA that is translated into protein, beginning at the start codon and ending at a stop codon.
Coding Sequence is the contiguous stretch of nucleotide triplets (codons) in a gene that encodes a polypeptide chain, spanning from the initiation codon (usually AUG) to a termination codon (UAA, UAG, or UGA) 1.
How It Works
The CDS is the information payload of a gene. During translation, the ribosome reads each three-nucleotide codon and recruits the corresponding aminoacyl-tRNA, assembling the polypeptide chain one amino acid at a time. The genetic code is degenerate — most amino acids are specified by multiple synonymous codons — and organisms exhibit strong preferences for particular codons that match their tRNA pools.
Codon usage bias has measurable effects on translation rate and accuracy. Genes using rare codons may stall ribosomes, trigger premature termination, or misfold due to altered co-translational folding kinetics. When expressing heterologous proteins, codon harmonization or optimization to match the host organism’s preferred codons can improve yield by 10- to 100-fold.
Beyond codon choice, the CDS nucleotide sequence affects mRNA secondary structure, which influences ribosome processivity and mRNA stability. Internal Shine-Dalgarno-like sequences in bacterial CDS regions can cause ribosome pausing. Careful CDS design must therefore consider both codon usage and local RNA structure.
Computational Considerations
Codon optimization tools (e.g., IDT Codon Optimization Tool, GenSmart) use species-specific codon usage tables and avoid sequence features that impair expression 2. Advanced algorithms co-optimize for codon usage, mRNA structure, GC content, and the absence of restriction sites, cryptic splice sites, and repeat elements simultaneously.
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Codon optimization algorithms redesign CDS nucleotide sequences for maximal expression in target hosts, while machine learning models predict protein folding and solubility from the coding sequence.