The 3D structure of the complete Escherichia coli ribosome with bound mRNA and tRNAs revealed that the very amino terminus of one protein (L27) does reach into the active site. This finding suggested a role for this protein in catalysis. To test this possibility, the nine amino acids at the L27 amino terminus that were in close proximity to the active site were eliminated by mutation. The following possible outcomes were found to be correct as A. The resulting cells produced ribosomes with reduced but detectable peptidyl transferase activity B. Region of the L27 protein contributes to peptidyl transferase activity C. The mutant ribosomes, didn’t synthesised wildtype levels of cells D. Vast majority of this increase in peptide bond formation is retained, even without the presence of L27 in the active site E. The most likely role for L27 is to correctly position one or more of the RNA components of the active site -triyambak.org