Definition of Yeast Artificial Chromosome (YAC) Libraries
Yeast Artificial Chromosome libraries are made by the systemic insertion of series of large human DNA fragments into a yeast strain capable of replicating the DNA insert truly, through multiple generations. The resulting organisms, when maintained under tightly controlled cataloging by the included DNA, can be maintained indefinitely as source organisms for ongoing and future research involving the genes inserted into that particular yeast organism.
How YAC Libraries Are Made
YAC libraries are difficult propositions even in though the first successful YAC libraries were created nearly 20 years ago. Some of the early successes in this field were published in 1990 by Hans Albertsen and his research team at the Paris, France Center for the Study of Human Polymorphism. Using the technique first pioneered by Burgess and Percival, the used an Epstein-Barr virus to insert human DNA genes into 10 different well-known research yeast strains.
The yeast and the genetic material both require significant preparation. Kits of the solutions and materials needed for this process are now available commercially for research organizations. BIO 101, Inc of San Diego California offers the eight different chemicals and three different yeast mediums required in a well-organized and standardized kit.
Using various procedures, the yeast is refined, then combined with the transformational DNA. Researchers generally prepare the DNA in advance for direct insertion or linked to a “carrier virus” capable of delivering the DNA into the Yeast Cell. These DNA sequences are often “tagged” or colored in such a way as to be visible upon microscopic examine. Such marking is key to readily identifying the success or failure of the transformation.
Once the transformations are complete, the key measure of success is the growth rate of the colonies. Yeast Artificial Chromosome libraries can only be useful and successful if the resulting organisms continue to replicate at a rate that provides a viable population for further experiments. When this is the case, the organisms are then stored in appropriate incubator environments, provided periodic fresh media to maintain the integrity and health of the available chimera organisms.
YAC libraries have various measures by which researchers evaluate them. In the case of Hans Albertsen et al, the resulting library consisted of over 50,000 clone colonies, with 95% of the kilobase pairs being over 250 in size. One of the most notable achievements of this team was that they achieved an average transformation size of 430 kilobase pairs. This was large enough to provide research-significant DNA commonality between the yeast organisms and the original human gene sets.
Keeping YAC libraries properly cataloged is one of the many functions of bioinformatics. The volume of information requires highly organized database management and sharing across organizations to avoid duplication of effort and enable proper usage of existing YAC libraries.