Origin of tetracycline efflux proteins: conclusions from nucleotide sequence analysis

Summary The sequences of six tetracycline efflux proteins and three transport proteins which have some resembalance to them were compared. The tetracycline efflux proteins fall into three families: (i) those encoded by pBR322, RP1, and Tn 10 (Escherichia coli); (ii) pT181 (Staphyloccoccus aureus) and pTHT15 (Bacillus subtilis); and (iii) tet347 (Streptomyces rimosus). There is global sequence homology within each of the first two families, but there is none between the families. The pT181/pTHT15 family shares close homology with the N‐terminal half of the methlenomycin A efflux protein (Streptomyces coelicor), while tet347 ressembles the C‐terminal half. Portions of the N‐terminal half of the Tn10‐encoded protein show significant resemblance to portions in the N‐terminal half of the pT181/pTHT15 family, but this sometimes occurs among transport proteins which do not have a common subtrate. Tetracycline efflux proteins, therefore, appear to have arisen on atleast two, or possibly three, separate occasions, probably from other transport proteins.