Transcripts of 259hiC6-1, -2, -3, -4 were detected using 259hiC6-1a/259hiC6-1b, 259hiC6-2a2/259hiC6-2b, 259hiC6-3a/259hiC6-3b and 259hiC6-4a/259hiC6-4b, respectively. The transcription of each hiC6 gene was also quantitatively evaluated by calculating the percentage of its cDNA clones in clones of total hiC6 cDNA. DNA fragments of hiC6 coding regions were generated by PCR using cDNA as the template and cloned
into the T-vector pMD18-T (Takara). For NJ-7, primers hiC6rt-3 and hiC6rt-6 (Table S1) were used; for UTEX259, primers hiC6rt-3 and hiC6rt-4 (Table S1) were used. Clones of hiC6 RT-PCR fragments were sequenced, and different hiC6 clones were counted and used for calculation of their percentages of the total hiC6 clones. Using total cDNA of C. vulgaris NJ-7 as the template, a PCR fragment containing the encoding BIBW2992 in vitro region of NJ7hiC6-3 was this website generated using primers hiC6pcc-1 and hiC6pcc-2. The PCR fragment containing 259hiC6-1 was generated using UTEX259 cDNA and a pair of primers hiC6pcc-2 and hiC6pcc-3. For 259hiC6-3 and 259hiC6-4, the primers hiC6pcc-1/hiC6pcc-2 were used. The PCR fragments were cloned into pMD18-T and sequenced, and clones of 259hiC6-3 and 259hiC6-4 were identified after sequencing. Using clones carrying different hiC6 genes as the templates and hiC6his-4/hiC6his-2 as the primers, PCR fragments for expressing mature HIC6 isoforms in E. coli were generated, cloned into pMD18-T
and confirmed by sequencing. The inserts in these plasmids were excised with NdeI and HindIII and cloned into pET21b (Novagen) for expression in E. coli BL21 (DE3). Expression of the HIC6 isoforms in E. coli was induced with 1 mM isopropyl-β-D-thiogalactopyranoside (IPTG) for 3–4 h at 37 °C. Cells broken by sonication were centrifuged at 13 000 g
for 10 min to remove cell Cepharanthine debris, and total soluble proteins were boiled for 10 min, followed by centrifugation at 13 000 g for 20 min. The recombinant HIC6 isoforms were purified from the supernatant using His·Bind resin (Novagen) under nondenaturing conditions according to the manufacturer’s recommendations. The eluted proteins were desalted using Microcon YM-10 (Millipore) centrifugal filters and diluted 25-fold with potassium phosphate buffer (pH 7.5). Protein concentrations were determined by Bradford’s method (Kruger, 2002) and confirmed by SDS-PAGE (Sambrook et al., 1989). The cryoprotective activities of HIC6 isoforms were assayed as described (Honjoh et al., 2000) with modifications. The freeze-labile enzyme LDH (Fluka) was diluted to 3 μg mL−1 with 10 mM sodium phosphate buffer (pH 7.5). Cryoprotectant solutions were prepared with potassium phosphate buffer (pH 7.5) and diluted to the indicated concentrations. A 500-μL aliquot of LDH was mixed with an equal volume of cryoprotectant solution and frozen at −20 °C for 24 h and thawed at 20 °C for 20 min.