Isoacceptor

Isoacceptor is a term used in molecular biology to describe a set of transfer RNA (tRNA) molecules that carry the same amino acid but possess different anticodons corresponding to different synonymous codons for that amino acid. Each isoacceptor is recognized and charged with the same amino acid by the organism’s aminoacyl-tRNA synthetase(s), enabling decoding of multiple codons that specify the same amino acid.

Isoacceptor tRNAs differ in their anticodon sequence and often in other sequence features or post-transcriptional modifications, which can influence their expression, stability, and interaction with ribosomes and synthetases. The existence of isoacceptors contributes to codon usage bias and translation efficiency, as cells modulate the abundance of different isoacceptors to optimize protein synthesis under different conditions.

Many amino acids have multiple isoacceptor tRNAs, with serine and leucine providing common examples. Each isoacceptor has a distinct anticodon that recognizes a subset of synonymous codons, while a single aminoacyl-tRNA synthetase charges all isoacceptors for that amino acid. Wobble base pairing at the third codon position expands codon recognition, allowing a tRNA anticodon to pair with more than one codon. The repertoire of isoacceptors varies among organisms and is shaped by genome size, codon usage, and regulatory needs.