Microcystin induction small Maf protein involve in transcriptional regulation of GST from freshwater mussel Cristaria plicata

The small Mafs, MafF, MafG and MafK play critical roles in morphogenesis and homeostasis through associating with Cap “n” Collar family of transcription factors. In this study, we tried to identify a small Maf protein in the freshwater mussel Cristaria plicata. The MafK cDNA of C. plicata, designated as CpMafK, was cloned from the hemocytes using degenerate primers by the rapid amplification of cDNA ends PCR. The full length cDNA of CpMafK is 2170 bp, which includes an open reading frame of 570 bp, encoding 189 amino acids. CpMafK possesses four conserved domains and shows a low level (54-63%) of sequence similarity to small Mafs from other species. The results of Real-time quantitative PCR revealed that CpMafK mRNA was constitutively expressed in tissues, and the highest expression level was in hepatopancreas. After microcystin challenge, the expression levels of CpMafK mRNA were up-regulated in hemocytes and hepatopancreas. The cDNA of CpMafK was cloned into the plasmid pET-32, and the recombinant protein was expressed in Escherichia coli BL21(DE3). CpMafK could combine to the promoters of CpGST1 and CpGST2 with high-affinity in vitro. Therefore, CpMafK could regulate the expression of detoxification.