Submitted to: Journal of Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 6, 2001
Publication Date: N/A
Interpretive Summary: Although the southern cattle tick (SCT) and the disease it transmits, babesiosis, were eradicated from the US after a 50-year eradication program of dipping cattle and temporarily vacating tick-infested pastures, they are still widespread in Mexico and other parts of America. Quarantine by vat dipping with chemical acaricides (pesticides that kill ticks and mites) has sprevented re-infestations in the US. But SCT has developed resistance to such acaricides. An understanding of mechanisms of pesticide resistance can help develop rapid, sensitive, and accurate methods for detecting pesticide resistance, which will lead to better pest management strategies and prolong the usefulness of the currently available pesticides. One way that arthropod pests develop resistance is through an increased rate of breakdown of pesticides. This is effected by changes in proteins called enzymes that break down these pesticides. One group of these enzymes, referred to as P450 enzymes, is involved in the degradation of poisons fro the environment, be it in the food or otherwise. These P450 enzymes are particularly important in the breakdown of pesticides in insect and tick pests, rendering them nontoxic. We have used sophisticated techniques of molecular biology to study the nature of these P450 enzymes in the SCT and have made discoveries that will be very useful in evaluating pesticide resistance. Our work will ultimately allow ranchers and the USDA Animal and Plant Health Inspection Service to better manage the SCT so as to assure that it does not re-infest US cattle herds.
We have isolated and sequenced a novel P450 gene (CYP319A1) from the cattle tick, Boophilus microplus. The CYP319A1 cDNA encodes a protein of 351 amino acids with an estimated molecular weight of 60.9 k. It contains all highly conserved motifs characteristics of P450 enzymes. Comparisons of deduced amino acid sequence with other CYP members shows that the CYP319A1 is more closely related to CYP4 family, but its overall identity to the CYP4 family is less than 40%. Therefore, it was assigned to a new P450 family by the P450 nomenclature committee. A pseudogene which shares high homology with the CYP319A1 was identified. Analysis of genomic sequence of the pseudogene indicated that the pseudogene contains two additional DNA inserts in the coding region, which disrupt the open reading frame. RT-PCR analysis showed that CYP319A1 is expressed in both susceptible and acaricide-resistant ticks.