OSBP and infection: These results suggested that there are positive correlations among the replication level, the membrane integrity, and the infectivity in PI4KB/OSBP-independent infection conferred by the 2B-Q20H mutation and that the 2B mutations have two distinct functions; the 2B-F17L mutation confers enhanced infectivity in PI4KB/OSBP-independent infection without affecting the replication level, while the 2B-Q20H mutation confers enhanced replication level and infectivity only via recessive epistasis between the 3A-R54W/2B-F17L mutations.