Complete nucleotide sequence of a gene conferring polymyxin B resistance on yeast: similarity of the predicted polypeptide to protein kinases

Polymyxin B is an antibiotic that kills sensitive cells by disrupting their membranes. We have cloned a wild-type yeast gene that, when present on a high-copy-number plasmid, renders the cells resistant to the drug. The nucleotide sequence of this gene is presented. A single open reading frame within the sequence has the potential to encode a polypeptide (molecular mass of 77.5 kDa) that shows strong homologies to polypeptides of the protein kinase family. The gene, PBS2, located on chromosome X, is not allelic to the previously described PBS1 gene (where PBS signifies polymyxin B sensitivity). Although pbs1 mutations confer resistance to high levels of polymyxin B, double mutants, pbs1 pbs2, are not resistant to the drug, indicating that PBS2 is essential for pbs1 activity. Models based on the proposed protein kinase activity of the PBS2 gene product are presented to explain the interaction between PBS1 and PBS2 gene products involved in conferring polymyxin B resistance on yeast cells.