λ as a Cloning Vector

Genes can be identified and cloned by complementanon of mutants, hybrrdtzation of nucleic acids, screening for their products, or systematic sequencing of genetic enttties. The chotce of the strategy to be applied for tsolating a gene of interest has to be taken in a space of parameters mcluding, for example, the availabthty of mutants and the stringency and spectfictty of selection procedures, the homology of nucleic-acid probes, the possibthty to unambtguously identify an encoded functton, the abundancy of the desired gene or its product with respect to the background (m other words, the size of the haystack in which to search for the needle), but also the effort and the amount of money that have to be spent to accomphsh the task Evaluatton of these parameters will then decide on the tools required, e g., DNA probes, antibodtes, or functional assays, and help to determine the vector/host system and type of library to be used