We use X-ray crystallography as our primary research tool to determine the three-dimensional structure of proteins and macromolecular complexes. We combine this structural information with biochemical, biophysical and functional studies to address the following objectives: (a) to understand the molecular basis of antibiotic resistance induced by mutations in ribosomal RNA or by the loss of post-transcriptional RNA methylation, (b) to understand the limits of structural robustness of ribosome functional centers in response to mutations of ribosomal RNA, and (c) to understand the structural determinants for specific recognition of multiple substrates by multi-specific enzymes..