A lactic acid bacterial regulatable expression system

摘要

An expression vector capable of being replicated in lactic acid bacterial cells is claimed comprising: a) promoter region comprising (i) a promoter sequence element whose function is regulatable by an environmental or growth condition factor and (ii) at least one further nucleotide sequence element which has a regulatory effect on the expression of a gene operably linked to the promoter region. b) at least one restriction site. The sequence of at least one of the elements of (i) and (ii) is modified relative to the sequence of the corresponding non-modified element. The modification of the at least one element results in that the expression of gene which is operably linked to the promoter region is increased at least two fold relative to the expression under essentially identical environment conditions of the same gene under the control of the corresponding non-modified promoter region. The regulation of the factors are not reduced or eliminated by the modification. The environmental or growth condition factor is selected from pH, growth temperature, oxygen content, temperature shift eliciting the expression of heat shock genes, the composition of the growth medium including the ionic strength/NaCl content, the presence/absence of essential cell constituents or precursors herefor, the growth phase of the bacterium and the growth rate of the bacterium. A lactic acid bacterium transformed by the above defined vector is claimed.