Efficient production of recombinant T7 endonuclease I using silkworm-baculovirus expression vector system

Recently, T7 Endonuclease I (T7E1) cleavage assay has been widely employed as an efficient approach for detecting mutations from CRISPR/Cas9 targeted samples. This enzyme is sufficient to detect single- and multiple-base mismatches from various heteroduplex DNA samples. However, T7E1 is quite expensive for researchers to use it only for screening mutations, especially in the condition of a large number of test samples. Regarding the production of this enzyme, to data, only the E. coli system has been reported and the highly overexpressed T7E1 seems toxic to the E. coli host cells. Thus, in this study, we tested whether the silkworm-baculovirus expression vector system (BEVS) is suitable to produce recombinant T7 Endonuclease I (rT7E1). The rT7E1 with N- or C-tags in cultured silkworm cells and silkworm pupae were successfully expressed. Our results demonstrated that the rT7E1-Ntag was highly expressed in silkworm pupae and we obtained rT7E1 proteins in high purity. Moreover, rT7E1 from silkworm-BEVS sufficiently recognized and cleaved the mismatches of designed and CRISPR/Cas9-mediated DNA substrates, which was equivalent to the commercial rT7E1 of the E. coli system. Taken together, our study would greatly support the genome-editing research by providing a cost-effective and active rT7E1 enzyme.