To investigate a possible intracellular coassociation of the paramyxovirus simian virus 5 (SV5) and human parainfluenza virus type 3 (HPIV-3) fusion (F) and hemagglutinin-neuraminidase (HN) glycoproteins in a living cell, without resorting to chemical crosslinking and antibody coimmunoprecipitation, we tagged the cytoplasmic N-terminus of SV5 HN with a RRRRR motif and HPIV-3 HN with a RRR motif for endoplasmic reticulum (ER) retention. In addition, we tagged the cytoplasmic C-terminus of SV5 and HPIV-3 F with a KK motif. The RRR- or RRRRR-tagged HN molecules were coexpressed in mammalian cells together with the homologous wt F proteins, and the KK-tagged F molecules were coexpressed with the homologous wt HN proteins, and in each case the transport of the wt 5 or HN molecules was investigated. The data suggest that an association of 5 and HN of sufficient affinity to alter the transport of the reporter molecule does not occur intracellularly in the ER or the Golgi apparatus.
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