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A full-length cDNA, with an open reading frame (ORF) of 1,449 bp, encoding a subunit of the γ-aminobutyric acid (GABA) -activated chloride channel was isolated from Plutella xylostella (L.) (Lepidoptera: Plutellidae) (GenBank accession no. EF156251). The subunit gene encoded a 483-amino acid polypeptide that showed 84% sequence identity with DmRdl subunit (U02042) (Drosophila melanogaster resistant to dieldrin). When expressed in Xenapus laevis oocytes, the subunit assembled as a functional homomeric complex activated by GABA and abamectin in a dose- dependent manner. The EC50 value of GABA was 0.49 mM (0.41-0.58) (n = 5). However, the responses to abamectin were very robust, with an EC50 of 4.85 μM (4.02-5.89) (n = 6), indicating that abamectin was >100-fold more potent in activating chloride currents than GABA. The results suggest that this subunit is vital to the formation of a functional channel and contains the binding site of abamectin. [ABSTRACT FROM AUTHOR]