Molecular Genetics

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• There are several types of vector DNA for molecular cloning.
  • Plasmids are extrachromosomal DNA elements.
    • Plasmids are used widely in cloning in bacteria.
    • In baker's/brewer's yeast, four types of plasmids are distinguished. These are all designed as shuttle plasmids, capable of replicating as plasmids in E. coli and in yeast.
      • YIP, yeast integrating plasmid
        = selectable marker +cloning sites
      • YRP, yeast replicating plasmid
        = YIP + ARS origin of replication
      • YEP, yeast expression plasmid
        = YIP + 2 micron origin of replication
      • YCP, yeast centromere plasmid
        = YRP + centromere sequence
  • Phages (viruses) are nucleic acids wrapped in protein coats.
    • Phages containing single-stranded DNA are used when subsequent manipulations (sequencing, site-specific mutagenesis) are performed on single-stranded DNA. Phagemids are plasmids that can be induced to produce phage particles containing single-stranded DNA.
    • The E. coli lambda phage contains 40 kbp of double-stranded DNA and can be used to carry DNA fragments up to about 20kbp. Cosmids are plasmids that contain part of lambda phage DNA, allowing the packaging of the DNA into lambda phage particles.
    • The P1 bacteriophage can accomodate more DNA than lambda and is the basis for PAC vectors.
    • Baculoviruses are used to carry DNA fragments into insect cells, usually for protein expression.
  • Artificial chromosomes contain all the elements that a DNA needs to function as a chromosome in the host organism.
    • YAC's are yeast artificial chromosomes. YAC = YCP + telomeres.
    • BAC's are bacterial artificial chromosomes
• Vectors can be thought of as an assemblage of modules that provide requirements essential for efficient molecular cloning.

Further information

• PAC's, BAC's and their hybrids are used extensively in genome mapping and sequencing projects.
• Information about some individual vectors is available through the vector database.