The quality and concentration of the total RNA was examined by agarose gel elec- trophoresis and by a spectrophotometer after processing with 1 U DNase I (Promega) at 37 C for 15 min to remove the trace amounts of genomic DNA. The concentration of each sample was then adjusted to the same level and stored at 80 C until the following experiment.
4.4. Subtractive hybridization
DSN-mediated normalization and subtractive hybridization (DNSH) was carried out following the method of Dai et al. [22], but with minor modifications. The primer pairs used in the DNSH method were the same as those in Dai’s study (for sequence information about the primers, see Table 1 in Dai et al. [22]). The efficiency of the subtractive hybridization was examined by amplifying the GAPDH gene using primer pairs GAPDH-F
(50 -GCCATCGCTATCTCCCTG-30 ) and GAPDH-R (50 -CCAGAAGTCA-
CAAACGCCTC-30 ).
4.5. Sequence analysis and blast search
After three rounds of PCR, >500 bp fragments were purified using the QIAquick Gel Extraction Kit (Qiagen). The products were then ligated with the vector pUCm-T (Takara). The PCR products of the plasmids were extracted from Escherichia coli culture using white colonies as inocula after blue/white screening. These plasmids were manipulated based on primer pairs M13F (50 -GTAAAACGACGGC CAG-30 ) and M13R (50 -CAGGAAACAGCTATGAC-30 ).
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