Lambda vectors for stable cloned gene expression

The bacteriophage lambda offers a unique opportunity concurrently to minimize segregational instability in recombinant systems by chromosomal integration of the cloned gene and to achieve high cloned gene expression during an abortive lytic phase. Lysis leads approximately to a 100-fold amplification of the cloned gene. Cell lysis in the lytic state is blocked by a specific mutation (Sam), allowing the cell to maintain its integrity, and lambda DNA packaging is blocked by other mutations (Wam, Eam) that keep cloned genes open to transcription. In the presence of these mutations, extremely high levels of cloned beta-galactosidase (more than 15% of total cell protein) have been obtained during abortive lysis from vectors found to be essentially 100% stable for over 75 generations in the lysogenic phase.