| Summary: | 碩士 === 國立清華大學 === 生命科學系 === 90 === Bacteriophage ΦA3 is isolated from Lactobacillus casei ATCC 393 by our lab. After sequence its partial chromosome DNA, we found a 1,351 bp insertion sequence ISLC3 (NCBI accession No. AF445084).
ISLC3 contains 37 bp inverted repeats and two overlapping open reading frames, named orfA and orfB, with an A7G motif in the overlapping region. ISLC3 orfB also contains a DD(35)E motif of transposase, so it is a member of IS3 family.
According to Southern hybridization, ISLC3 is present 1-6 copies in the Lactobacilli genome. Southern hybridization analyses the distribution of the new insertion sequence ISLC3.
Sequence analysis of 4 independent genomic copies of inverse PCR products indicated that the direct repeats of ISLC3 is non-detected. Formation of circle junction is shown here to occur a 25 bp deletion of IRL and create a new stronger promoter.
After analyzing ISLC3 characteristics and distribution, the further research is trying to construct a suicide integration vector, which carries an erythromycin resistance gene within ISLC3. By transforming the vector into L. casei ATCC 393, the erythromycin resistance gene may be transposed into the Lactobacillus chromosome. If the experiment is successful, it is possible to choosing another gene, such as virus epitop gene, to develop Lactobacillus oral vaccine.
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