This invention provides a method for obtaining a nucleotide sequence that
codes for the active part of a polypeptide specifically active for larvae
of S. littoralis. The method comprises hybridizing at least one
nucleotide probe to DNA from a strain of B. thuringiensis active against
S. littoralis, wherein at least one nucleotide probe is derived from the
5' part of a restriction fragment of a gene for .delta. endotoxin of B.
thuringiensis strain aizawa 7-29, isolating the DNA from the strain of B.
thuringiensis active against S. littoralis that hybridized to the probe,
cloning the isolated DNA into a vector, and purifying the vector to
thereby obtain the nucleotide sequence that codes for the active part of
a polypeptide specifically active for larvae of S. littoralis, wherein
the specifically active polypeptide has (1) a specificity index of less
than 1.0 and (2) a higher specific toxic activity towards S. littoralis
than the native crystal proteins of the strains aizawai 7-29 or berliner
1715.
