APPENDIX E 
At tne upper left is a cell containing chromosomal DNA and several small 
independent genetic elements. These small independent DNA molecules are isolated 
from the cel I and serve as one portion of the recombined DNA, the segment 
termed the vector. Such elements may be circular DNA molecules such as 
plasmids, or viral DNAs, and they can be cleaved, as shown, by restriction 
endonuclease (or by other tneans) to yiela linear duplex DNA strands with either 
sticky ends, or ends that can be made sticky by appropriate modification. 
In most experiments, the recombinant DNA will finally be reinserted into cells 
of the same species from which the vector was isolated. It is the genetic 
information encoded in the DNA of the vector which ultimately will be respon- 
sible for the continued existence and replication of the recombined DNA in 
the recipient cell. At the upper right of Figure I another cell is shown as 
a rectang I e . Th i s ce I I will serve as the source of DN^ to be joined to the 
vector. Tnis DNA is termed the foreign DNA, and the rectangular cell can 
represent a cell from any living species. As shown here, the foreign DNA 
might contain chromosomal DNA or independent DNA elements, or both. It too 
can be cleaved to yield fragments of various lengths with sticky ends, or 
ends that can be made sticky. The foreign DivlA fragments are then Joined 
to the vector DNA, usually by duplex formation at the sticky ends, followed by 
closure of the internucleotide bonds with polynucleotide ligase. The recombinant 
DNA is subsequently inserted into a recipient cell, wnich is called the host. 
Again, the host cell will most likely be of the same species as that used 
for the isolation of the vector. The cells are then placed under conditions 
where either they or the recombined DNA can replicate. 
Appendix E — 3 
