Biology Reference
In-Depth Information
Figure 9.3
Examples of modified
P
-element vectors. A) The Carnegie 20 vector contains a 7.2-kb
segment of DNA coding for the
rosy
gene. It contains a polylinker for inserting exogenous DNA and
retains the 31-bp inverted repeats (IR, dark arrows). This vector cannot transpose without a helper
element because it cannot make transposase. B) The helper element, p
π
25.7 wings clipped, pro-
duces transposase, but 23 bp of inverted repeat has been deleted at one end so this vector cannot
insert into the chromosome.
to be determined. Different lines are likely to have different levels of expression
because of position effects (
Spradling and Rubin 1983, Levis et al. 1985
).
9.8 Using
P
-Element Vectors
9.8.1 Transposon Tagging
The insertion of
P
into a gene allows the isolation and cloning of that gene
if
the altered gene results in altered phenotype in
D. melanogaster
. Because many
P
strains contain 30-50 copies of
P
, transposon tagging should be carried out in
D. melanogaster
strains lacking endogenous
P
elements.
Transposon tagging
relies on the development of two specially designed
P
vectors (
Cooley et al. 1988
). The goal is to introduce a
single P
into the germ
line of flies
lacking P
. One vector, called “jumpstarter,” encodes transposase
and mobilizes a second vector, called “mutator,” to transpose (
Figure 9.4
). The
