DNA itself is infected and can commence infection by inoculating on the surface of the host plant. CaMV genome contains eight closely packed reading frames. There are only two small intragenic regions which can be discarded and replaced by the insert. If any other region is removed or when a large sized insert is used, no infection takes place.

Thus, only a small size of insert of few hundred bp can be used as insert. This requirement of a small sized insert imposes limitations on the use of this vector for gene transfer. Even the use of helper virus coding for the lost genes when a large insert is placed will not restore their functions. The reasons are not clear.