TABLE 1.

Summary of the effects of point mutations introduced into two furin sites on S protein cleavage, induction of cell-cell fusion, and recovery of infectious rIBV

S gene mutation siteNamePrediction of furin cleavageaCleavagebCell-cell fusioncRecovery of rIBVd
S1/S2 site (positions 531-539)2nd site (positions 684-692)S1/S22ndTryTry+
Wild typeWT GTRRFRRSI PSSRRRRSV +++++++++
S1/S2M1 GTAAFAASI PSSRRRRSV ++++++
Δ1 GT-----SI PSSRRRRSV ++++++
2ndM2 GTRRFRRSI PSSAAAASV +
Δ2 GTRRFRRSI PSS----SV +
M2.1 GTRRFRRSI PSSPRRRSV ++++
M2.2 GTRRFRRSI PSSRAAASV ++
M2.3 GTRRFRRSI PSSARAASV ++
M2.4 GTRRFRRSI PSSAARASV ++
M2.5 GTRRFRRSI PSSAAARSV +++++
Both sitesM1 + 2.1 GTAAFAASI PSSPRRRSV +++
OtherS(Δ538-690) GTRRFRR-- -------SV +None
  • a The predicted cleavage position is in boldface.

  • b Cleavage at two furin sites in HuH-7 cells expressing pKT-S(1-789)Fc is indicated by + for yes and − for no cleavage.

  • c Cell-cell fusion at neutral pH in Vero cells expressing pKT-S is indicated by +++ for strong, ++ for mild, + for weak, and − for no induction.

  • d Recovery of infectious rIBV in Vero cells is indicated by + for yes and − for no.