Libraries

Libraries are collections of clones of DNA, often present in plasmids in E. coli or in bacterial viral genomes. The use a researcher has for a library dictates the source of the DNA fragments and the vector DNA (plasmid or viral) into which fragments are cloned. A library can be screened to find a clone of interest.


Types of libraries

• Genomic library. A collection of fragments representing all DNA in the chromosomes of a cell.
  
  
• cDNA library. Collection of DNAs representing the genes expressed in cell or tissue type. cDNA libraries are made by converting mRNA transcripts isolated from tissues or cells into DNA fragments that can then be cloned into a vector. For example, a muscle cDNA library contains copies of genes expressed in muscle cells and will contain many clones different from those found in a brain cDNA library.
  
  
• cDNA expression libraries. A collection of expressed genes cloned into a vector next to a regulatory region so that the protein will be produced under conditions controlled by the experimenter. For example, DNA can be cloned into a vector to create a fusion protein used to test a gene product for interaction with other proteins.
  
  
• Electronic libraries. With the human genome project, the DNA sequence from several model organisms as well as humans is being determined. This information serves as a virtual DNA library that can be analyzed via computer.
  

	Fundamentals of Cell Function
	Cloning DNA
	Libraries
	Screening Libraries
	Gene Expression
	Elimination of Gene
	Interactions with Other Proteins