Construction and Screening of Cosmid Libraries

Cosmid libraries still are an important tool for cloning large genomic regions. Although other Escherichia coli -based vector systems like bacteriophage PI, bacterial artificial chromosomes (BACs), and PI-based artificial chromosomes (PACs) allow the cloning of longer inserts, they are more difficult to handle (1 ). Therefore, even if they are frequently used for the initial generation of libraries from large genomes, cosmid vectors are often still required to generate libraries with smaller, more manageable pieces or libraries from limited DNA amounts, such as bands isolated from pulsed-field gels (2 ).