We characterized thioredoxin reductase 1 (TrxR1) from Chironomus riparius 
(CrTrxR1) and studied its expression under oxidative stress. The full-length 
cDNA is 1820bp long and contains an open reading frame (ORF) of 1488bp. The 
deduced CrTrxR1 protein has 495 amino acids and a calculated molecular mass of 
54.41kDa and an isoelectric point of 6.15. There was a 71bp 5' and a 261bp 3' 
untranslated region with a polyadenylation signal site (AATAAA). Homologous 
alignments showed the presence of conserved catalytic domain 
Cys-Val-Asn-Val-Gly-Cys (CVNVGC), the C-terminal amino acids 'CCS' and conserved 
amino acids required in catalysis. The expression of CrTrxR1 is measured using 
quantitative real-time PCR after exposure to 50 and 100mg/L of paraquat (PQ) and 
2, 10 and 20mg/L of cadmium chloride (Cd). CrTrxR1 mRNA was upregulated after PQ 
exposure at all conditions tested. The highest level of CrTrxR1 expression was 
observed after exposure to 10mg/L of Cd for 24h followed by 20mg/L for 48h. 
Significant downregulation of CrTrxR1 was observed after exposure to 10 and 
20mg/L of Cd for 72h. This study shows that the CrTrxR1 could be potentially 
used as a biomarker of oxidative stress inducing environmental contaminants.