Cautionary note on ribonuclease activity of recombinant PR-10 proteins

We studied the biochemical properties of three splicing isoforms of PR-10 from rubber tree (Hevea brasiliensis) and found that purified recombinant HbPR10 can cause RNA degradation in vitro, a well-known activity described for many PR-10 proteins. This ribonuclease activity was observed for all three HbPR10 splicing isoforms and is abolished by boiling. However, inclusion of a negative control proteins revealed that ribonuclease activity rather originates from RNases that are copurified from E. coli, which are overlooked by traditionally used controls such as heat inactivation, RNase inhibitors and negative control proteins obtained with different procedures. The crucial control proteins are missing for at least nine reports on ribonuclease activity in PR-10 proteins published by different laboratories worldwide, indicating that proper controls are frequently overlooked in ribonuclease assays. The raised cautionary note applies to several PR-10 proteins with proclaimed ribonuclease activities and call for the use of different assays and mutant PR-10 proteins as control.