Yeast ( YAC ) and Human ( HAC ) Artificial Chromosome Clones

Abstract

Artificial chromosome vector systems in yeast and bacteria have facilitated the increasingly rapid pace of mapping and sequencing of complex genomes. Traditional bacterial cloning systems have remained important for the study of relatively short clones, but for the cloning of very large deoxyribonucleic acid (DNA) segments yeast artificial chromosomes (YACs) have completely replaced earlier bacterial systems, including lambda phage‐based cosmids. YACs comprise cloned DNA fragments ranging from 50 kb to more than 1 million base pairs, along with sequences that render them capable of growth in yeast or bacteria. YACs provide the additional advantage of permitting direct isolation of a targeted genomic region as a circular molecule from complex genomes by transformation‐associated recombination. Moreover, YAC cloning has allowed the propagation of large tandem repeat arrays and entire bacterial genomes. By taking advantage of the efficient yeast recombination system, YAC clones can be further modified and used for functional studies of full‐length genes and for the study of huge centromeric DNA repeat regions that are not yet analysed or included in the genome assemblies of human and other organisms. Key Concepts: Basic structure of vectors used in the construction of artificial chromosomes that can replicate in yeast, bacteria and human cells. Utilities of artificial chromosomes. Isolation of complete genes and large DNA segments, including repetitive chromosomal regions. Targeted recombination‐based cloning of genes and highly repetitive regions. Reconstruction of large DNA regions by recombination among multiple YAC clones.