1. Yeast Artificial Chromosome
YAC
Yeast Artificial Chromosome

2. Definition:
Yeast artificial chromosome (YAC) Is a vector used to clone DNA fragments larger than 100 kb and up to 3000 kb. YACs are useful for the physical mapping of complex genomes and for the cloning of large genes. First described in 1983 by Murray and Szostak

3. Structure :
The centromere, which is required for the chromosome to be distributed correctly to daughter cells during cell division.
Two telomeres, the structures at the ends of a chromosome, which are needed in order for the ends to be replicated correctly and which also prevent the chromosome from being nibbled away by exonucleases.
The origins of replication, which are the positions along the chromosome at which DNA replication initiates, similar to the origin of replication of a plasmid.
A YAC vector contains a yeast telomere (TEL) at each end, a yeast centromere sequence (CEN), a yeast selectable marker for each arm (here, TRP1 and URA3), a sequence that allows autonomous replication in yeast (ARS), and restriction sites for cloning.

4. The structure and use of a YAC vector
YAC is built using an initial circular plasmid, which is typically broken into two linear molecules using restriction enzymes; DNA ligase is then used to ligate a sequence or gene of interest between the two linear molecules, forming a single large linear piece of DNA.

5. Applications for YAC vectors
for genes that are too long to be cloned as a single fragment in an E. coli vector. Several important mammalian genes are greater than 100 kb in length (e.g., the human cystic fibrosis gene is 250 kb)
to studies of the functions and modes of expression of genes that had previously been intractable to analysis by recombinant DNA techniques.
are equally important in the production of gene libraries.
routinely used to clone 600 kb fragments, and special types are able to handle DNA up to 1400 kb in length, the latter bringing the size of a human gene library down to just 6500 clones.

7. This is a photo of two copies of the Washington University Human Genome YAC Library. Each of the stacks is approximately 12 microliter plates. Each plate has 96 wells, each with different yeast clones.

9. References:
Gene cloning and DNA analysis an introduction T.A. Brown.6th Ed
Molecular Cloning. A Laboratory Manual, Third Edition - Sambrook and Russell-Vol.2
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