On The Cover (August 14, 2015):The NMR structure of the Escherichia coli threonylcarbamoyl-AMP synthase TsaC (teal). TsaC has been shown to bind l-threonine and ATP to catalyze the reaction forming the intermediate threonylcarbamoyl-AMP (yellow) in the biosynthesis of the tRNA modification threonylcarbamoyladenosine (purple, Protein Data Bank entry 1FEQ). For details, see the article by Harris et al., pages 20032-20043.