The mutant effects of a keV range nitrogen ion （N＋） beam on enzyme-producing probiotics were studied, particularly with regard to the induction in the genome. The electron spin resonance （ESR） results showed that the signal of ESR spectrum existed in both implanted and non-implanted spores, and the yields of free radicals increased in a dose-dependent manner. The ionic etching and dilapidation of cell wall could be observed distinctly through the scanning electron microscope （SEM）. The mutagenic effect on genome indicated that N＋ implantation could make base mutation. This study provided an insight into the roles low-energy ions might play in inducing mutagenesis of micro-organisms.
In order to obtain three isoforms of apolipoprotein E （apoE）, the eDNA encoding apoE3 was obtained by RT-PCR from normal human liver tissue, Site-directed mutagenesis was used to obtain the cDNAs encoding apoE2 and apoE4 isoforms. The 3 cDNAs were subcloned into vector pGEM-3Z and verified by DNA sequencing. The expression recombinant which can express the target protein as a （His） 6-tagged fusion was constructed by subcloning apoE eDNA into vector pTT-PL, The purified proteins were gained by Ni-NTA column, The SDS-PAGE results revealed the 6 His fusion proteins （apoE2, apoE3 and apoE4） were correctly expressed and purified successfully.
