Characterization of a cry2A gene cloned from an isolate of Bacillus thuringiensis serovar sotto.

A cry2A-type gene, designated as cry2(SKW), was cloned from Bacillus thuringiensis serovar sotto SKW01-10.2-06, and some unique features of the gene were revealed. The cry2(SKW) gene encoded a polypeptide of 635 residues with a predicted molecular mass of 71,137 Da. Cry2(SKW) had 95.4% identity with Cry2Aa in amino acid sequence and was two residues longer than Cry2Aa. Two open reading frames (ORFs), designated as orf1 and orf2, were present upstream of the cry2(SKW) and showed high homology with the corresponding ORFs in the cry2Aa operon. The Orf2 from SKW01-10.2-06 contained a region of repeated sequences. However, unlike Cry2Aa, Cry2(SKW) formed the cuboidal crystalline inclusions when the cry2(SKW) gene was expressed in an acrystalliferous B. thuringiensis strain in the absence of the upstream ORFs. Furthermore, Cry2(SKW) was less toxic to a lepidopteran species, Bombyx mori, than Cry2Aa in spite of high homology between the two proteins.