A type of cloning vector that has some features of true chromosomes and is used to clone relatively large fragments of DNA. Bacterial artificial chromosomes (BACs) are based on the F (fertility) plasmid found naturally in E. coli bacteria (see sex factor). They can accommodate inserts of foreign DNA up to about 200 kilobase (kb) in length. Also included are several bacterial genes necessary for replication of the plasmid by the host cell and a gene (usually for resistance to an antibiotic) that allows selection of BAC-containing cells. Similar to BACs are PACs (P1 artificial chromosomes), which incorporate phage P1 elements. Larger DNA fragments are cloned using yeast artificial chromosomes (YACs). These are linear vectors derived from a circular plasmid found naturally in baker's yeast (Saccharomyces cerevisiae) and capable of accommodating DNA inserts of up to 1000 kb. YACs have a centromere, enabling them to attach to the mitotic spindle of their yeast host and undergo normal segregation during cell division. They are also engineered with telomeres, the DNA sequences that cap either end of a chromosome. Thus YACs behave like mini-chromosomes. They are used for cloning eukaryotic genes or gene segments, for making DNA libraries of organisms with large genomes (e.g. mammals), and for studying gene function.
Subjects: Biological Sciences.