The 23SrRNA is a 2904 nt long (in E. coli) component of the large subunit (50S) of the bacterial/archean ribosome. The ribosomal peptidyl transferase activity resides in domain V of this rRNA, and this domain is the most common binding site for antibiotics that inhibit translation. A well-known member of this antibiotic class, chloramphenicol, acts by inhibiting peptide bond formation, with recent 3D-structural studies showing two different binding sites depending on the species of ribosome. Linezolid and quinupristin-dalfopristin also bind to the 23S rRNA, and cross-resistance has been demonstrated between these antibiotics. Compared to 16S rRNA genes, 23S rRNA genes typically have higher sequence variations including insertions and/or deletions 
^Mueller F, Sommer I, Baranov P, Matadeen R, Stoldt M, Wöhnert J, Görlach M, van Heel M, Brimacombe R (2000). "The 3D arrangement of the 23 S and 5 S rRNA in the Escherichia coli 50 S ribosomal subunit based on a cryo-electron microscopic reconstruction at 7.5 Å resolution". J Mol Biol. 298 (1): 35–59. doi:10.1006/jmbi.2000.3635. PMID10756104.
^Pei A, Nossa CW, Chokshi P, Blaser MJ, Yang L, et al. (2009) Diversity of 23S rRNA Genes within Individual Prokaryotic Genomes. PLOS ONE 4(5): e5437. doi: 10.1371/journal.pone.0005437