Tremendous intron length differences of the BmKBT and a novel BmKBT-like peptide genes provide a mechanical basis for the rapid or constitutive expression of the peptides

► A novel BmKBT-like peptide, BmKBy, was identified from Mesobuthus martensii Karsch. ► Both BmKBT and BmKBy possess potent toxicity in mammal, but weak toxicity in insect. ► Two genes, of which intron sizes differ in 5.8 folds, code for BmKBT, whereas one gene with an intron of 1312 bp codes for BmKBy. ► The tremendous difference of the intron lengths of the BmKBT genes provides a mechanical basis for either constitutive expression or rapid generation of the toxic peptides in response to different signals.