Then, neo2 from pMNMM2 was removed by SalI and SmaI and replaced with the amplified neo5 cassette, resulting in pMNMM3 (Fig. 1A). The DNA sequence of pMNMM3 can be found in the Additional file 1. A Cre-recombinase (DDBJ/EMBL/GenBank AAG34515) encoding DNA, which was optimized for Tetrahymena codon-usage, was synthesized (MR. GENE GmbH, Regensburg, Germany) and named cre1. An HA sequence including a short two-amino acid linker www.selleckchem.com/products/z-vad-fmk.html (GA) was added at the N-terminus

of cre1 by PCR amplifying the cre1 coding sequence using PrimeStar HS DNA Polymerase (Takara) with the primers HA-GA-Cre-NdeFW and Cre-MluRV. Then, this PCR product was cloned into NdeI and MluI sites of pMNMM3 to produce pMNMM3-HA-cre1 (Fig. 1B). The MTT1-5′-1-neo5-MTT1-5′-2-HA-cre1-MTT1-3′ construct was excised from the vector backbone by digesting pMNMM3-HA-cre1 with XhoI and SpeI. The DNA sequence of pMNMM3-HA-cre1 can be found in the Additional file 1. Construction of the loxP-neo4-loxP-EGFP-TWI1 construct by PCR First, the loxP-neo4-loxP sequence was generated by PCR amplifying the neo4 cassette with the primers LoxNeoFWXho and LoxNeoRV. These primers had loxP sequences at their 5′-termini. PrimeStar HS DNA Polymerase (Takara) was used for all PCR reactions in this section.

In parallel, EGFP was amplified by PCR with the primers LoxGFPFW and LoxGFPRVBam using pOptiGFP as a template. pOptiGFP has a EGFP sequence optimized for Tetrahymena codon-usage (Kataoka et al. submitted with this manuscript). A short complementary Temozolomide clinical trial sequence was designed at the 3′-terminus of loxP-neo4-loxP and the 5′-terminus of EGFP. Then, loxP-neo4-loxP and EGFP PCR products were concatenated by overlapping PCR with LoxNeoFWXho and LoxGFPRVBam. The resulting loxP-neo4-loxP-EGFP was cloned into the BamHI and XhoI sites of pBlueScript SK(+) to create ploxP-neo4-loxP-EGFP. The loxP-neo4-loxP-EGFP-TWI1 construct (see Fig. 3A) was generated by PCR. The 5′-flanking

selleck products and N-terminal regions of the TWI1 gene were amplified using the primers TWI15LoxFW + TWI15LoxRVATGplus and TWI1 NGFPFW + TWI1NGFPRV, respectively, resulting in TWI1-5F and TWI1-N. Also, loxP-neo4-loxP-EGFP was excised from ploxP-neo4-loxP-EGFP using BamHI and XhoI. This fragment had overlapping sequences with the 3′ terminus of TWI1-5F and with the 5′- terminus of TWI1-N, respectively. Finally, the three DNA segments, TWI1-5F, loxP-neo4-loxP-EGFP and TWI1-N were combined by overlapping PCR using TWI15LoxFW and TWI1 NGFPRV. The PCR product loxP-neo4-loxP-EGFP-TWI1 was purified and used directly for the transformation of Tetrahymena. Construction of Tetrahymena strains CRE556 and loxP-neo4-loxP-EGFP-TWI1 Biolistic gun transformation was performed as described [2] to introduce the constructs into the macronucleus by homologous recombination. The B2086 and CU428 wild-type strains were transformed with the digested pMNMM3-HA-cre1 and the loxP-neo4-loxP-EGFP-TWI1 PCR products, respectively.