lox sites

In neurobilogy we leared about LoxP sites. These are areas in the DNA that correlate to each other. Thye work in the presence of CRE recombinase in order to flip the DNA sequence between the paired Lox sites, or cut it out completely. When the LoxP sites are facing the same direction, they loop the DNA between the two sites and cut the sequence between the two sites, and one of the lox sites, out of the genome. This results in two strands of DNA, each with one of the paired lox sites. CRE recocmbinase can only work on one pair of LoxP at a time, so cutting out of Lox of a pair is a perminant and irreversable change. On the other hand, if the two paired LoxP sites are facing opposite directions, they form a loop in the DNA and flip the DNA in between the LoxP sites around. For example, if the DNA inbetween the LoxP sites is in the anti-sense direction, the flipped DNA would then be in the sense direction. This is a method used by neurobiologists who want to insert a sequence of DNA into specific cells. The neuoscientist would insert a sequence of DNA in the antisense direction, between two inverted LoxP sites. The DNA sequence would be taken up by all cells in the area, but only cells expressing CRE recombinase would be able to flip the DNA sequence into the sense direction in order to express it.