So apparently researchers have succeeded in finding a highly reduced RNA-only ribosomal core capable of catalyzing multiple successive rounds of peptide bond formation, resulting in 9-mers of polylysine:
Ribosomal protein synthesis is a central process of the modern biological world. Because the ribosome contains proteins itself, it is very important to understand its precursor and evolution. Small ribozymes have demonstrated the principle of “RNA world” hypothesis, but protein free peptide ligase remains elusive. In this report, we have identified two fragments in the peptidyl transfer center that can synthesize a 9-mer poly-lysine in a solution contains Mg2+. This result is deduced from isotope-shifting in high resolution MS. To our best knowledge, this is the longest peptide oligo that can be synthesized by a pure ribozyme. Via single molecule FRET experiments, we have demonstrated the ligase mechanism was probably by substrate proximity via dimerization. We prospect that these RNA fragments can be useful to synthesize template free natural and non-natural peptides, to be model system for peptidyl transfer reaction mechanism and can shed light to the evolution of ribosome.
This is noteworthy because all previous attempts to get fully protein depleted ribosomal RNA to catalyze peptide bond formation had so far proved unsuccessful, even though synthetic ribozymes had previously been shown to be capable of that.