| Abstract: | In previous systems for in vitro packaging of lambda 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 lambda 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 lambda DNA efficiently and (iii) are easy to prepare. Using the cos- in vitro packaging system we show that packaging of lambda 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. |
