Is every protein encoded by just one gene? Beadle and Tatum proposed the “one gene, one enzyme” hypothesis in the 1940s, and this was later modified to “one gene, one protein”, i.e. that one gene codes for one protein. Have any exceptions to this emerged subsequently? Are there single proteins, parts of which are encoded by separate genes?

There _are_ proteins encoded by more than one gene.

It would be a **heterodimer** protein of **quaternary** structure. One famous example would be haemaglobin, which is assembled from alpha and beta sub-units.

Also, one gene is capable of coding for multiple proteins!

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