Tet Protein Hybrids

In their recent letter to the editor (1), Drs. Stanton, Humphrey, Scott, and Flint raised an important point in regard to naming tetracycline resistance determinants in view of the discovery of naturally occurring interclass hybrid proteins. In addition to the current definition of a new gene, i.e., less than 80% amino acid identity to another known tetracycline resistance determinant, we endorse their suggested nomenclature for hybrid determinants and proteins, e.g., Tet O/W (hybrid of Tet O and Tet W) and Tet W/O/W (hybrid of Tet O and Tet W, which has partial Tet O sequence between Tet W ends). The finding of hybrid Tet proteins makes it important, therefore, to sequence entire tet genes to identify such hybrids. The question arises as to how many amino acids corresponding to a second class will define a hybrid. Looking at their data, we suggest that 50 amino acid residues in a single stretch could be appropriate.