are totally 122 bp long intron in the genome copy. Multiple alignment of GSTz amino acid sequence with other GSTzeta showed the existence of conserved characteristic motif (SSCX[WH]RVIAL) of zeta subgroup in Tetrahymena GSTz. Change in expression of GSTz mRNA level under the hydrogen peroxide and cold (4 • C) stresses with time intervals was analyzed with semi-quantitative RT-PCR method. While there was no change at the level of GSTz mRNA under the hydrogen peroxide stress, the amount of mRNA was increased with time under the cold stress. After incorporation of seven necessary multiple point mutations (TAA > CAA or TAG > CAG) on mRNA protein coding region of GSTz gene for the protein expression in E. coli, the recombinant fragment was ligated to pET16b expression plasmid and transformed into E. coli BL21-DE3. SDS-PAGE analysis of recombinant 6xHis-TtGSTz protein (24 kDa) showed that it is successfully purified not only by nickel agarose but also by glutathion-sepharose 4B. The Western blot analysis showed also that both anti-His and anti-GST antibodies recognized the purified recombinant 6xHis-TtGSTz. In conclusion, the preliminary results presented here suggest that 6xHis-TtGSTz could be used as a dual tag in the Tetrahymena expression vectors to improve the purification of proteins from Tetrahymena.