Major advances in our understanding of molecular biology have been ach
ieved over the last 10 years since the first cloning and sequencing of
a crystal protein gene in 1981. A family of five cry genes are now kn
own which differ in their spectrum of activity. Other toxin genes are
known but not yet cloned and sequenced. A wide range of alternative ho
sts have been used to produce recombinant toxins including plants. Rec
ent studies have related the structural components of the gene to part
icular loci.