Hypothetical protein

In biochemistry, a hypothetical protein is a protein whose existence has been predicted, but for which there is no experimental evidence that it is expressed in vivo.

The usual scenario involving a hypothetical protein is in gene identification during genome analysis. When the bioinformatic tool used for the gene identification finds a large open reading frame without an analog in the protein database, it returns "hypothetical protein" as an annotation remark. The function of a hypothetical protein can also be predicted by domain homology searches with various confidence levels.