Structural Biochemistry/DNA recombinant techniques/Artificial Chromosomes/Yeast Artificial Chromosomes (YAC)

Yeast Artificial Chromosomes (YAC)

Similar to bacterial artificial chromosomes (BACs), yeast chromosomes can be used as host chromosomes in the process of DNA cloning Like BACs, YACs (yeast artificial chromosomes) are synthetic chromosomes with integrated DNA fragments from a foreign source. The difference between YACs and BACs is that YACs does not use a plasmid such as the F factor in E.Coli. Instead YACs use specific regions of the yeast chromosome. The yeast chromosomes contain all the necessary parts for replication which includes the following: a centromere, telomere ends, DNA site markers, restriction enzymes EcoRI and BamHI and the origin of replication. With the mentioned components, a foreign fragment of DNA can be spliced into any regions between the telomeres and centromeres. A DNA fragment is spliced by using restriction enzyme EcoRI.The cleaved DNA fragment can range from 100 to 1000kb, thus YACs allow for the insertion of larger DNA sequences which can result in greater efficiency. After the DNA fragment is cleaved, the yeast artificial chromosomes are also digested by the two restriction enzymes; EcoRI and BamHI. The fragments are then recombined at the EcoRI sites and are joined together by DNA ligase resulting in a new chromosome with the inserted DNA fragment.Once the foreign DNA fragment is spliced into the yeast chromosome, replication of DNA begins as DNA polymerase begin to elongate the DNA strand at the origin of replication site during cell division/replication by mitosis. When the host chromosome is elongated, the foreign DNA fragments get elongated along with the host chromosome. The result of this method is similar to using BACs, which is a huge colony of yeast cells with the fragmented DNA. The cloned fragments of DNA in the yeast chromosomes can then be used for genetic research such as gene mapping or simply put into a gene library for further use.