Molecules that mimic DNA could be turned into a new family of antibiotics, say Danish scientists. The molecules are based on peptide nucleic acid (PNA). In PNA, nucleotide bases like those in DNA and ribonucleic acid (RNA) are attached to a backbone of linked amino acids. Researchers at the University of Copenhagen say that they have now produced PNA molecules that have base sequences designed to stick to key parts of RNA in the food-poisoning bacterium Escherichia coli . They hoped this would stop the bacteria from making proteins and kill them. In tests conducted so far, the PNA proved to as good as the antibiotic tetracycline at finishing off the bacteria ( Proceedings of the National Academy of Sciences , Vol 95).