Yeast Artificial Chromosome (YACs)

Yeast Artificial Chromosome (YACs)

These are linear DNA molecules similar to yeast chromosome. Recombinant YACs are made by ligating large fragments of genomic DNA and then the resultant plasmid is introduced into yeast by transformation. The vector carries selection marker, DNA sequences called as telomere, so that the product can be stabilized inside the yeast cell, an origin of replication called autonomous replication origin, ARS. Large size of DNA can be inserted into YAC vectors, usually between 250kilobases to 400kilobasepairs. Large size of mammalian genomic libraries is also made with approximately 1 megabasepairs of foreign inserts. Insertion of foreign DNA into the cloning site inactivates a mutant expressed in vector DNA and formation of red rather than white colonies by yeast strain is observed. Thus transformants are identified as red colonies, which grow in yeast that is mutant for TRP1 and URA3, which ensure that the cell has received an artificial chromosome and with both the telomeres since it is complimented for both the mutations. And the colony also contains foreign DNA because it is red in color.