Mojave rattlesnakes (Crotalus scutulatus scutulatus) lacking the acidic subunit DNA sequence lack Mojave toxin in their venom.

The venom composition of Mojave rattlesnakes (Crotalus scutulatus scutulatus) differs in that some individuals have Mojave toxin and others do not. In order to understand the genetic basis for this difference, genomic DNA samples from Mojave rattlesnakes collected in Arizona, New Mexico, and Texas were analyzed for the presence of DNA sequences that relate to the acidic (Mta) and basic (Mtb) subunits of this toxin. DNA samples were subjected to PCR to amplify nucleotide sequences from second to fourth exons of the acidic and basic subunits. These nucleotide sequences were cloned and sequenced. The nucleotide sequences generated aligned exactly to previously published nucleotide sequences of Mojave toxin. All DNA samples analyzed generated product using the basic subunit primers, and aligned identically to the Mtb nucleotide sequence. However, only 11 out of the 14 samples generated a product with the acidic subunit primers. These 11 sequences aligned identically to the Mta nucleotide sequence. The venom from the three snakes whose DNA did not amplify with the acidic subunit primers were not recognized by antibodies to Mojave toxin. This suggests that snakes with venom lacking Mojave toxin also lack the productive nucleotide sequence for the acidic subunit in their DNA.