Low Levels of Expression of Cry Genes,Wild Type Genes,Plant Coding Regions,Plant Polyadenylation

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	Low Levels of Expression of Cry Genes - The low expression level of cry genes seems to be due to the presence in them of sequences not commonly found in plant coding regions. For example, cryI(A)b contains: (1) localized A + T rich regions resembling plant introns, (2) 18 potential plant polyadenylation signal sequences, (3) 13 ATTTA sequences, which destabilize mRNA, and (4) codons rarely used in plants.
CryIA(b) and cryIA(C) sequences have been either partially or fully modified to remove the above difficulties as far as possible without affecting the amino acid sequences of the Cry proteins encoded by them. The transgenic plants containing these modified cry genes showed greatly enhanced levels of expression; in case of tobacco and tomato, there was a 100-fold increase over the expression level of the wild type genes.