Vectors λ200g and λ200c: two useful derivatives of λ2001

Abstract We describe the construction and uses of two new phage λ, replacement vectors. Both are modifications of 2001 which allows selection of cloned inserts by the Spi − phenotype, following the replacement of a gam + filler fragment. Vector λ 200g has a second gam gene with an amber mutation in its right arm which enables the selection of clones with inserts in the normal way in Su° host bacteria and the maintenance of their genetic stability by subsequent growth in Su + strains. Vector λ200c is designed for complementation studies. It contains a cat gene and the attP site of λ. Recombinants can be inserted into the bacterial chromosome or into an episome with the aid of appropriate helpers.