misincorporation

Misincorporation is the inadvertent inclusion of an incorrect monomer—such as a nucleotide during DNA or RNA synthesis, or an amino acid during protein synthesis—into a growing polymer. In DNA replication, misincorporation occurs when a DNA polymerase inserts the wrong nucleotide opposite a template base. Most such errors are corrected by the polymerase's 3' to 5' exonuclease proofreading activity and by post-replicative mismatch repair. If not corrected, misincorporation can produce point mutations, some of which are deleterious or can be silent depending on the change and its location.

During transcription, RNA polymerase can also misincorporate nucleotides, producing altered mRNA molecules. The error rate of transcription is higher than DNA replication, but the changes are not heritable and are usually rapidly degraded by cellular quality control or translation.

At the level of translation, misincorporation refers to incorrect amino acids being incorporated into a polypeptide, arising from mischarged tRNAs or codon-anticodon mispairing. The ribosome exerts proofreading, aided by aminoacyl-tRNA synthetases that edit incorrect aminoacylation. Misincorporation can yield proteins with altered function or stability. Some antibiotics exploit translational misreading to impair microbial protein synthesis and growth.

Consequences of misincorporation include genetic mutations, defective proteins, and altered cellular phenotypes. Organisms employ multiple layers of fidelity mechanisms to minimize errors, and the biological impact of misincorporation depends on frequency, cellular context, and repair capacity.