The pre-membrane protein (prM) is a caperone protein for the
envelope protein during intracellular protein assembly by masking
and inactivating envelope protein E fusion peptide. prM is matured
in the host Golgi. prM (nucleotide positions 477..977) contains the
sequence for small envelope protein M/matrix protein M (nucleotide
positions 753..977), which has a role in viral budding and
activation of mitochondrial apoptotic pathway via M ectodomain.