Envelope protein part of the entry-fusion complex responsible for the virus membrane fusion with host cell membrane during virus entry. Also plays a role in cell-cell fusion (syncytium formation). Part of a stable entry-fusion complex (EFC) which is at least composed of proteins A16, A21, A28, G3, G9, H2, J5, and L5. Formation of the viral membrane is necessary for the assembly of the complex. Component of the mature virion (MV) membrane. The mature virion is located in the cytoplasm of infected cells and is probably released by cell lysis (By similarity). Belongs to the poxviridae A16/G9/J5 family.