Abstract: Bacillus thuringiensis subsp. Morrisoni strain Rpp02 isolated by researchers in our laboratory was highly toxic to several kinds of insect pests. Results of PCR analysis indicated that strain Rpp02 contained the cry1Ac gene, and subsequently a novel cry1Ac gene was cloned from this strain by PCR techniques. The results of sequence analysis showed that the novel gene cry1Ac20, named by B.thuringiensis Pesticidal Crystal Protein Nomenclature Committee, contained an open reading frame of 3 534 nucleotides encoding a protein of 1 177 amino acids with a predicted molecular mass of 133.144 kDa and isoelectric point of 4.952. Compared with other known cry1Ac genes, cry1Ac20 has shown as high as 99% nucleotide sequence homology. Bioassay showed that the toxic protein appeared high insecticidal activity against Pieris rapae L., and the corrected mortality was 88.78% 48 h after feeding with leaves immersed in cultures containing transformants.

Key words: Bacillus thuringiensis, cry1Ac20 gene, cloning, expression