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KMID : 1160620000050030153
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Preventive Nutrition and Food Science
2000 Volume.5 No. 3 p.153 ~ p.159
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Expression of β-Galactosidase Gene of Lactococcus lactis ssp. lactis ATCC 7962 in Lactococcus lactis ssp. lactis MG1363
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Park Rae-Jun
Lee Jung-Min
Chang Hae-Choon
Chung Dae-Kyun
Lee Jong-Hoon
Lee Hyong-Joo
Kim Jeong-Hwan
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Abstract
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A 4.4 kb DNA fragment encompassing lacA (galactoside acetyltransferase) and lacZ (β-galactosidase) genes from Lactococcus lactis ssp. lactis ATCC 7962 (L. lactis 7962) was introduced into a Lac- strain, Lactococcus lactis ssp. lactis MG1363 (L. lactis MG1363) by using a lactococcal expression vector, pMG36e and expression level of lacZ was examined. Growth rates and β-galactosidase (β-gal) activities of MG1363 cells carrying recombinant plasmid, pMLZ3, on M17 broth containing different carbon sources (1%, w/v) were examined. Contrary to the expectations, MG1363 [pMLZ3] grown on lactose showed the lowest enzyme activity (17 units) and cells grown on galactose had the highest β-gal activity (41 units). Cells grown on glucose had intermediate activity (33 units). These activities are about one tenth of the values observed in L. lactis 7962 where lacZ is present as a single-copy gene in the chromosome. When the cellular concentrations of lacZ transcript were examined using slot blot hybridization, it was found that MG1363 [pMLZ3] produced sufficient amounts of transcript. These results indicate that either proteolytic degradation of β-gal or other regulatory mechanisms prevent the translation or accumulation of β-gal in L. lactis MG1363 cells. In regard to regulation, the presence of the ccpA gene in L. lactis MG1363 was confirmed by Southern blot.
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KEYWORD
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Lactococcus lactis, β-galactosidase, expression vector, ccpA
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