FUNCTIONAL INTERACTION OF PARAMYXOVIRUS GLYCOPROTEINS - IDENTIFICATION OF A DOMAIN IN SENDAI VIRUS HN WHICH PROMOTES CELL-FUSION

The cell fusion activity of most paramyxoviruses requires coexpression of a fusion protein (F) and a hemagglutinin-neuraminidase protein (HN ) which are derived from the same virus type, To define the domain of the HN protein which interacts with the F protein in a type-specific m anner, a series of chimeric HN proteins between two different paramyxo viruses, Sendai virus (SN) and human parainfluenza virus type 3 (PI3), was constructed and coexpressed with the SN-F protein by using the va ccinia virus T7 RNA polymerase transient-expression system, Quantitati ve assays were used to evaluate cell surface expression as well as fus ion-promoting activities of the chimeric HN molecules. A chimeric HN p rotein [SN(140)] containing 140 N-terminal amino acids derived from SN -HN and the remainder (432 amino acids) derived from PI3-HN was found to promote cell fusion with the SN-F protein, In contrast, a second ch imeric HN with 137 amino acids from SN-HN at the N terminus could not promote fusion with SN-F, even though the protein was expressed on the cell surface, A construct in which the PI3-HN cytoplasmic tail and tr ansmembrane domain were substituted for those of SN in the SN(140) chi mera still maintained the ability to promote cell fusion. These result s indicate that a region including only 82 amino acids in the extracel lular domain, adjacent to the transmembrane domain of the SN-HN protei n, is important for interaction with the SN-F protein and promotion of cell fusion.