Yeast artificial chromosome

This is the process that was initially used for the Human Genome Project, however due to stability issues, YACs were abandoned for the use of bacterial artificial chromosome [2] The bakers' yeast S. cerevisiae is one of the most important experimental organisms for studying eukaryotic molecular genetics.

[1] Beginning with the initial research of the Rankin et al., Strul et al., and Hsaio et al., the inherently fragile chromosome was stabilized by discovering the necessary autonomously replicating sequence (ARS);[2] a refined YAC utilizing this data was described in 1983 by Murray et al.[3] The primary components of a YAC are the ARS, centromere [3], and telomeres [4] from S. cerevisiae.

By being able to insert large fragments of DNA, YACs can be utilized to clone and assemble the entire genomes of an organism.

Due to these issues, the Human Genome Project ultimately abandoned the use of YACs and switched to bacterial artificial chromosomes, where the incidence of these artifacts is very low.

In addition to stability issues, specifically the relatively frequent occurrence of chimeric events, YACs proved to be inefficient when generating the minimum tiling path covering the entire human genome.

Also, due to the nature of the reliance on sequence tagged sites (STS) as a reference point when selecting appropriate clones, there are large gaps that need further generation of libraries to span.

This is a photo of two copies of the Washington University Human Genome YAC Library. Each of the stacks is approximately 12 microtiter plates. Each plate has 96 wells, each with different yeast clones.
Schematic of the pBR322 plasmid generated in the Boyer Lab at UC San Francisco by Bolivar and Rodriguez in 1972. It is one of the first and most widely utilized vectors, and the foundation for the YACs created by Murray and Szostak in 1983 The plasmid contains ampicillin and tetracycline resistance genes, and a suite of restriction enzyme target sites for inserting DNA fragments.