increase in cellulose production is presumed to
be solely due to the acquisition of a lacZ gene. This assumption
was supported by the result of the L-galactosidase
activity assay. Strain ITz3 has on the average 160-
fold higher enzyme activity (4 U against 644 U) than
strain ITDI 2.1, whereas the di¡erence in speci¢c enzyme
activity between the two strains was 27 times (Table 2).
Other possible e¡ects after transposition of the gene
should also be considered since mini-Tn10:lacZ :kan is
promoterless. For instance, in the case of some insertion
sequence (IS) elements, insertion to a particular site or
locus can turn o¡ or on the expression of other nearby
genes. Moreover, the orientation or direction in which the
IS element is inserted is signi¢cant in some other case such
that inserted in one direction the IS element turns o¡
genes nearby; or inserted in the opposite direction, a nearby
gene that is unexpressed may be turned on [22].
The speci¢c enzyme activities of ITz3 following growth
in sucrose, lactose and whey substrates, without the use of
isopropyl thiogalactose (IPTG) for induction of lacZ, were
not signi¢cantly di¡erent from each other (Table 2, lower
half). This is an indication that the lacZ gene was constitutively
transcribed in ITz3 and not regulated by the available
carbon source or addition of IPTG. It may be possible
that the lacZ gene got inserted in a promoter of a locus
in the direction in which transcription of the structural
genes were turned on all the time resulting in the enzyme
production becoming constitutive. This is the case of IS2
element insertion in the operator^promoter region of the
galactose operon.
increase in cellulose production is presumed tobe solely due to the acquisition of a lacZ gene. This assumptionwas supported by the result of the L-galactosidaseactivity assay. Strain ITz3 has on the average 160-fold higher enzyme activity (4 U against 644 U) thanstrain ITDI 2.1, whereas the di¡erence in speci¢c enzymeactivity between the two strains was 27 times (Table 2).Other possible e¡ects after transposition of the geneshould also be considered since mini-Tn10:lacZ :kan ispromoterless. For instance, in the case of some insertionsequence (IS) elements, insertion to a particular site orlocus can turn o¡ or on the expression of other nearbygenes. Moreover, the orientation or direction in which theIS element is inserted is signi¢cant in some other case suchthat inserted in one direction the IS element turns o¡genes nearby; or inserted in the opposite direction, a nearbygene that is unexpressed may be turned on [22].The speci¢c enzyme activities of ITz3 following growthin sucrose, lactose and whey substrates, without the use ofisopropyl thiogalactose (IPTG) for induction of lacZ, werenot signi¢cantly di¡erent from each other (Table 2, lowerhalf). This is an indication that the lacZ gene was constitutivelytranscribed in ITz3 and not regulated by the availablecarbon source or addition of IPTG. It may be possiblethat the lacZ gene got inserted in a promoter of a locusin the direction in which transcription of the structuralgenes were turned on all the time resulting in the enzymeproduction becoming constitutive. This is the case of IS2element insertion in the operator^promoter region of thegalactose operon.
การแปล กรุณารอสักครู่..
