Although our studies provide support for the REE role of SL6 in TBEV it is unclear if SL6-like structures of MBFV act similarly as functionally significant REE. However, the remarkable resemblance of the WNV SL6-like structure to TBFV SL6 suggests that it might serve a similar function, at least in one virus group. However, a final conclusion for the MBFV and also for the more distant NKV or PABV groups is not possible ahead of further functional studies.