Wolfgang Piepersberg

A second streptomycin resistance gene from Streptomyces griseus codes for streptomycin-3″-phosphotransferase

Two genes, aphE and orf, coding for putative Mr 29,000 and Mr 31,000, proteins respectively, were identified in the nucleotide sequence of a 2.8 kbp DNA segment cloned from Streptomyces griseus N2-3-11. The aphE gene expressed streptomycin (SM) resistance and a SM phosphorylating enzyme in S. lividans strains. The two genes were found to be in opposite direction and seemed to share a common region of transcription termination. The aphE gene shows significant homology to the aph gene, encoding aminoglycoside 3′-phosphotransferase, APH(3′), from the neomycin-producing S. fradiae. The enzymatic specificity of the aphE gene product was identified to be SM 3″-phosphotransferase, APH(3″). The primary structure of the APH(3″) protein is closely related to the members of the APH(3′) family of enzymes. However, the APH(3″) enzyme did not detectably phosphorylate neomycin or kanamycin. There is only low similarity of the protein to the APH(6) group of SM phosphotransferases. An evolutionary relationship between antibiotic and protein kinases is proposed.

Evolution of Antibiotic Resistance and Production Genes in Streptomycetes

Increasing amounts of DNA and protein sequence data became available recently from genetic studies on antibiotic production and resistance in both producing and resistant bacteria. This sequence information mirrors the current state of a long-term evolution which obviously very early have lead to complete pathways, which in later stages have diversified or degenerated, or became individualized especially in the actinomycete group of microorganisms. Examples are the pathways for betalactams polyketides, and aminoglycosides (Hershberger et al., 1989; Cundliffe, 1989; Martin and Liras, 1989). Also, convergently evolved genetic traits have to be postulated. The resistance genes coding for antibiotic or target site modifying enzymes (phospho-, acetyl-, adenylyl-, and methyltransferases) seem to have a central position in the overal development which created the secondary metabolic pathways for the respective — mostly ribosomal targeted — antibiotics and the concomitant gathering of genes to larger clusters (Piepersberg et al., 1988). Also, they could be derived from other control genes such as for regulatory protein kinases or for ribosomal processing.