Genetic localization and regulation of the maltose phosphorylase gene, maIP, in Lactococcus lactis

Maltose phosphorylase (MP) from Lactococcus lactis was purified and the cor responding gene was cloned and expressed in Escherichia coli, The The isoel ectric point of the pure enzyme was determined to be 7.0. According to zymo gram analysis and SDS-PAGE, the native MP was shown to be a INTRODUCTION mo nomeric enzyme with a molecular mass of 75 kDa, A polyclonal antiserum was produced to assess the regulation of the gene encoding MP in Lc. lactis. Ac cording to immunoblot analysis, synthesis of the enzyme was markedly repres sed by both glucose and lactose in the growth medium. When the lactococci w ere cultivated in the presence of other sugars, including maltose, trehalos e or galactose, there was a pronounced expression of the MP gene. In additi on, when the cells were grown in media without any added sugar, there wits also pronounced expression of the enzyme, according to immunoblot analysis and specific activity data. These results indicated that no particular suga r specifically induces the gene encoding MP, however, an effect of glucose on MP expression was demonstrated by performing fermentations in the presen ce of both maltose and glucose. When glucose was added to maltose-grown lac tococci in the mid-exponential growth phase, both the specific activity and amount of MP per millilitre of cell extract decreased rapidly. The genetic locus for the MP gene was found to be in the vicinity of the region encodi ng a possible regulator belonging to the Lacl-GalR family of transcriptiona l regulators. Furthermore, this genetic location was separated from the pre viously characterized maltose-inducible and glucose-repressible beta -phosp hoglucomutase (beta -PGM) gene. The different genetic loci for the genes en coding MP and beta -PGM explains the different gene regulation behaviour.