From the wikipedia article referenced earlier: "Peptidyl transferase activity is not mediated by any ribosomal proteins but by ribosomal RNA (rRNA), a ribozyme.

From the wikipedia article referenced earlier: "Peptidyl transferase activity is not mediated by any ribosomal proteins but by ribosomal RNA (rRNA), a ribozyme. This RNA relic is the most significant piece of evidence supporting the RNA World hypothesis."