Proteincoding

Protein-coding refers to genes or sequences that are translated into proteins. In genomics and molecular biology, protein-coding DNA or RNA sequences are transcribed into messenger RNA and then translated by ribosomes into polypeptides, which fold into functional proteins. Protein-coding regions constitute a major portion of many genomes, though a substantial fraction of the genome is noncoding.

In eukaryotes, protein-coding genes typically include exons and introns. Exons are the portions that encode amino acids and are retained in the mature messenger RNA after splicing; introns are removed before translation. The coding sequence, or CDS, spans from a start codon to a stop codon and determines the amino acid sequence of the protein. In contrast, many prokaryotic genes lack introns and often have simpler, continuous coding regions. Alternative splicing in eukaryotes can produce multiple protein isoforms from a single gene.

Expression begins with transcription of the gene by RNA polymerase, followed by RNA processing events such as 5' capping and 3' polyadenylation in eukaryotes. The mature mRNA is translated by ribosomes, which interpret codons—sets of three nucleotides—to specify amino acids. Translation typically starts at an AUG start codon and ends at a stop codon (UAA, UAG, or UGA). Transfer RNAs deliver amino acids in the order specified by codons.

Proteins produced from protein-coding genes perform diverse roles, including enzymatic catalysis, structural support, signaling, and transport. Gene annotation and genome projects focus on identifying protein-coding regions, while proteomics analyzes the actual proteins present in cells. Some genomic elements once labeled as protein-coding are reevaluated with new evidence, and noncoding RNAs can sometimes contribute to coding potential under particular conditions.