Gene II product of an aphid-nontransmissible isolate of cauliflower mosaic virus expressed in a baculovirus system possesses aphid transmission factor activity.

A new baculovirus expression system was used to express the gene II which encodes the 18-kDa aphid transmission factor (ATF) protein of two isolates of cauliflower mosaic virus (CaMV), the aphid-transmissible (AT+) Cabb B-JI and the aphid-nontransmissible (AT-) CM1841 isolates. ATF activity was shown to be associated with the baculovirus expression product of CaMV gene II from both the AT+ and the AT- isolates. No differences could be detected in the stability of the P18s from AT+ and AT- isolates expressed in the baculovirus system. These results indicate that the AT- phenotype of CM1841 isolate might not be due to a defective P18 but to an insufficient concentration of it in infected plant tissue.