A series of plasmids were constructed to examine the effects of p19 and orf1-orf2 genes from Bacillus thuringiensis on Cyt1Aa synthesis and inclusion formation. The plasmids expressed the cyt1Aa gene along with either p19 or orf1-orf2, or each of them coordinatively with p20 in the acrystalliferous strain of B. thuringiensis subsp. israelensis 4Q7. No effect on the expression of Cyt1Aa protein was found when P19 or Orf1-Orf2 co-expressed with Cyt1Aa. However, when including p20 gene, the constructs with p19 or orf1-orf2 gene produced lower yield of Cyt1Aa proteins than without p19 or orf1-orf2 gene. Electron microscopy observation and bioassay showed that P19 and Orf1-Orf2 have no influence on the crystal size and toxicity of Cyt1Aa protein. It is presumed that P19 and Orf1-Orf2 might have negative effects on Cyt1Aa synthesis in B. thuringiensis.
