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کروموزوم مصنوعی مخمر
Vectors into which the target gene is cloned for delivery into the host cell can be specialized plasmids designed to be maintained in the eukaryotic host, such as the yeast 2µm plasmid; hostspecific viruses, such as the insect baculovirus; or artificial chromosomes, such as the yeast artificial chromosome (YAC).
There are three main classes of S. cerevisiae expression vectors: episomal, or plasmid, vectors, integrating vectors, and YACs.
A YAC is designed to clone a large segment of DNA (100 kilobase pairs [kb]), which is then maintained as a separate chromosome in the host yeast cell.
The YAC system is highly stable and has been used for the physical mapping of human genomic DNA, the analysis of large transcription units, and the formation of genomic libraries containing DNA from indi vidual human chromosomes.
A YAC vector mimics a chromosome because it has a sequence that acts as an origin of DNA replication (ARS), a yeast centromere sequence to ensure that during cell division each daughter cell receives a copy of the YAC, and telomere sequences that are present at both ends after linearization of the YAC DNA for stability (Fig. 3.27).
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