Yeast Artificial chromosomes YACs, Plasmid Vectors, Phage Vectors, Cosmid Vectors Sequences, Lower Eukaryotes

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Yeast artificial chromosomes (YACs)

We know that in plasmid vectors, sequences upto 10-15 kbp, in lambda (λ) phage vectors sequences upto 22kbp and in cosmid vectors sequences upto 40kbp can be cloned. Yeast artificial chromosome (Y AC) vectors, mentioned earlier allow cloning of sequences that are several hundred kilo base pairs (upto 1000 kbp = I Mbp) long.

These long molecules of DNA which may represent whole chromosomes in lower eukaryotes with very small genomes can be cloned in yeast by ligating them to vector sequences that allow their propagation as linear artificial chromosomes.

These long DNA molecules can be generated and allow construction of comprehensive libraries (with large DNA segments) in microbial hosts. With the isolation of mammalian telomere and centromere, mammalian artificial chromosomes (MACs) have also been produced.

An artificial yeast chromosome vector

YACs have two disadvantages. (i) Cloning efficiency is low (1000 clones/μg DNA as against 10⁶ - 10⁷ clones/μg DNA for cosmids), thus making it impractical to generate complete genomic libraries through the use of YACs.

(ii) It is not possible to recover large amount of pure insert DNA from individual clones; selective amplification of YACs DNA has recently allowed this problem to be overcome. Both these problems have been overcome in BACs and PACs described earlier.

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BACs and PACs as Vectors for Cloning large DNA Segments (100-300 kb) Bacterial Artificial Chromosomes (BACs) P1-derived Artificial Chromosomes (PACs) Plant and Animal viruses as Vectors Plant Viruses (Cauliflower Mosaic virus or CaMV and Geminiviruses) Animal Viruses Transposons as Vectors Transposons of Higher Plants (Ac/Dc or Mul of Maize) Transposons of drosophila (P elements) YAC and MAC Vectors for Cloning very large DNA Segments (1000 kb) Yeast Artificial Chromosomes (YACs) Mammalian Artificial chromosomes (MACs) Expression Vectors Promoters Nopaline Synthase (nos) Promoter from T-DNA Dual Promoter of Mannopine Synthase (mas) genes 1 and 2 35S Promoter of CaMV Polyhedrin Promoter from Baculovirus Expression Cassettes Baculovirus and Expression Vector System for Insect Cells Virus Expression Vectors for Mammalian Cells Binary and Shuttle Vectors