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Encyclopedia of Genetics, Genomics, Proteomics and Informatics

pp 2121-2122

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YAC

Refers to yeast artificial chromosome vectors equipped with a yeast centromere and some (Tetrahymena) telomeres in a linear plasmid containing selectable markers, ARS (autonomously replicating sequence) for the maintenance and propagation of eukaryotic DNA inserts in cloning of larger than 200 kb size sequences.YACs play an important role in identifying contigs in physical mapping of larger genomes, as well as in in situ hybridization, map based gene isolation, etc. The rate of instability of YAC has been estimated to be about 2%. In mitotic yeast cells YACs behave like other chromosomes. Meiosis can be analyzed by tetrads although recombination appears to be reduced. YACs may be maintained through some cell divisions in the mouse cytoplasm and behave like double minute chromosomes or they may be integrated into the mouse chromosomes. anchoring, contigs, YAC library, in situ hybridization, chromosome walking, pulsed field gel electrophoresis, DM; Peterson KR 1999 Methods Enzymol 306:186;Brown WR et al 2000 Trends Biotechnol 18:218; Adam G et al 1997 Plant J 11:1349; Ragoussiz J, Monaco AP 1996 Methods Mol Biol 54:157, see Fig. Y1.
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Figure Y1.

Top: A circular yeast plasmid with Tetrahymena telomeres. A segment of the pBR322 prokaryotic plasmid contains the replicational origin and the Amp R gene (selectable in E. coli for ampicillin resistance). The ARS (autonomous replication sequence), cloned centromere of yeast chromosome 4 (CEN 4), restriction enzyme recognition sites where the plasmid can be opened for insertion and later ligation are shown. The TRP1 (tryptophan) AND URA 3 (uracil) genes of yeast serve to ascertain that both arms are present and the transformant can synthesize tryptophan and uracil. A piece of the plasmid between the two Bam sites and also the yeast HIS (histidine) gene are deleted. Because of the pBR322 sequences, this vector replicates in E. coli as well as in eukaryotic cells. All details are not shown and the diagram is not to scale. Other YAC vectors are similar but not identical with this model. Bottom: Completed linear YAC. (Modified after Burke DT et al 1987 Science 236:806)

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