In Vitro Packaging of DNA

In the normal growth cycle of bacteriophage lambda, the proteins that ultimately form the head of the phage particle are assembled into an empty precursor of the head (prehead); the phage DNA is replicated separately and then inserted into the empty head particles—a process known as packaging. A number of phage gene products play an important role in this process. Amongst these are:

(i)	The E protein, which is the major component of the phage head; mutants that are defective in this gene are unable to assemble the preheads, and therefore accumulate the other, unassembled, components of the phage particle as well as the other proteins involved in packaging.
(ii)	The D and A proteins, which are involved in the packaging process itself. Mutants that are defective in these genes are able to produce the preheads, but will not package DNA. This results in the accumulation of empty preheads.