The present invention further relates to the expression system which furthermore includes a helper plasmid to drive the expression of translocons to facilitate improved periplasmic secretion of the over-expressed recombinant protein.

Novel compositions are Agrobacterium strains that have been engineered to comprise at least two binary vector plasmids in addition to a helper plasmid comprising the vir functions.

An improved method for preparing chimeric silk fibers employing the transgenic silkworms disclosed herein is also provided, the method employing a piggyBac based vector system and a helper plasmid.

A piggyBac vector system is used to transform mutant silkworm, in the presence of a helper plasmid, to incorporate the chimeric spider silk gene into the silkworm to provide a stable transformant.