Abstract
In previous systems for in vitro packaging of λ DNA, phages are produced from the packaging components as well as from added DNA. We have developed a new genetic strategy for in vitro packaging that bypasses this endogenous phage problem. Our system employs a single bacterial strain whose λ prophage codes for all of the packaging proteins but is deleted for cos, the packaging origin. Crude extracts of the single lysogen: (i) are virtually free from endogenous phages, (ii) package added λ DNA efficiently and (iii) are easy to prepare. Using the cos − in vitro packaging system we show that packaging of λ linear monomers is a second-order reaction, but that packaging from concatemers prepared by annealing or ligation is first order. We conclude that in our cos − system, linear monomers are a poor substrate for in vitro packaging but that packaging from concatemers works well.
Published Version
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