Vector, cloning

A DNA molecule originating from a virus, a plasmid (see below) or the cell of a higher organism into which another DNA fragment can be integrated without loss of the vector's (carrier's) capacity for self-replication.

Cloning vectors are used to introduce foreign DNA into host cells, where that DNA can be reproduced (cloned) in large quantities.</P> Examples of cloning vectors are plasmids, cosmids, and yeast artificial chromosomes (YACs):</P> > >Plasmid: Autonomously (self) replicating, extrachromosomal circular DNA molecules, distinct from the normal bacterial genome and usually not essential for cell survival.

Some plasmids are capable of integrating into the host genome.

A number of artificially constructed plasmids are used as cloning vectors.

>Cosmid: An artificially constructed cloning vector containing a gene (the cos gene) of the virus called phage lambda.

Cosmids can be packaged in lambda phage particles for infection into the bacteria E.

Coli; this permits the cloning of larger DNA fragments than can be introduced into bacterial hosts using plasmid vectors.

>Yeast artificial chromosomes (YAC): A vector (carrier) created and used in the laboratory to clone pieces of DNA, a YAC is constructed from the telomeric (end), centromeric, and replication origin sequences needed for the replication of the cloned DNA within yeast cells.

</LI></UL> Cloning vectors are often recombinant DNA molecules containing DNA sequences from several sources.