Oxazolidinones are antibacterial agents that act
primarily against gram-positive bacteria by inhibiting
protein synthesis. The binding of oxazolidinones to 70S
ribosomes from Escherichia coli was studied by
both UV-induced cross-linking using an azido derivative
of oxazolidinone and chemical footprinting using dimethyl
sulphate. Oxazolidinone binding sites were found on both
30S and 50S subunits, rRNA being the only target. On 16S
rRNA, an oxazolidinone footprint was found at A864 in the
central domain. 23S rRNA residues involved in oxazolidinone
binding were U2113, A2114, U2118, A2119, and C2153, all
in domain V. This region is close to the binding site of
protein L1 and of the 3′ end of tRNA in the E site.
The mechanism of action of oxazolidinones in vitro was
examined in a purified translation system from E. coli
using natural mRNA. The rate of elongation reaction of
translation was decreased, most probably because of an
inhibition of tRNA translocation, and the length of nascent
peptide chains was strongly reduced. Both binding sites
and mode of action of oxazolidinones are unique among the
antibiotics known to act on the ribosome.