Re: how do DNA vectors work, in the process of carrying genes into nuclear DNA?

Hi Belinda

Sorry for the delay: I've just moved from Belgium to Sweden. I was a bit 
busy. :-)
A DNA vector is a piece of DNA containing the gene you're interested in. 
It's a carrier. This may or may not integrate the gene into the DNA of the 
host cell. In bacteria, for instance, you often add DNA vectors which stay 
clear of the bacteria's own DNA, a bit like a satellite. There are then 
several ways to add the new gene into the existing gene pool, which is 
especially important when you want to add the gene to a mold, a fly, a 
plant or a mouse as they will sulk any bit of DNA that isn't in their 
chromosomes.

One way is to make sure the DNA is present when there is a lot a "repair" 
going on: for instance when the ovule has just been fertilised by a sperm, 
but the nuclei haven't merged yet. Then the cells own repair system is 
tricked into incorporating even the foreign DNA if this has been injected 
in one of the nuclei. This is often done with mice.
With flies one usually uses a special kind of small ring-formed DNA 
(plasmid). This comes from something called "mobile genetic elements" 
which many animals have naturally. It's a stretch of DNA that can 
occasionally jump around from one place to another in the chromosomes. By 
letting a gene of our making hitch a ride, it can be added to the nuclear 
DNA.
In plants a method of choice is to use another plasmid, which comes from a 
bacterium that causes galls. The way the bacterium does it is by injecting 
into the plant a plasmid carrying the genes which will force the plant 
cells to grow uncontrollably, like a cancer. On either side of the genes 
in the plasmid are small stretches of DNA that match certain sites in the 
plant DNA. That's where the plasmid and plant DNA will merge. Now, if we 
remove the "cancer-forming" genes and replace them with a gene we want 
there: there you are! We have another kind of carrier. This is close to 
what one hopes to be able to do in human gene therapy. The herpes virus, 
for instance, does the same kind of trick, finding a place to hide in our 
own DNA. If we would remove everything that makes the herpes virus nasty 
and give it something useful to deliver, one could possibly cure such 
diseases as Alzheimer's and diabetes. The big problem is to get the virus 
to deliver at the right address!

I hope this answers your question. If you want more detail, you are 
welcome to wite again.
Greetings,

Erik von Stedingk