Three X mutants were constructed based on the Q(-) mutant in order to enhance their productivity and stability in an Escherichia colil bacteriophage lambda system. The newly constructed bacteriophage mutants named lambda SNU1, lambda SNU2, and lambda SNU3 were Q(-)S(-), Q(-)W(-)E(-), and Q(-)S(-)W(-)E(-) mutants, respectively. Compared to all of the mutants, lambda SNU1 turned out to be the best with regards to higher protein expression and better genetic stability. Mechanisms by which these attributes are achieved have been discussed. The high productivity of P90c/lambda SNU1 for the recombinant protein was due to the high copy number of lambda DNA and high translational efficiency. This mutant phage lambda SNU1 can be used to provide a high level of stability and productivity of the cloned gene particularly for long-term continuous operation. (c) 2006 Elsevier Ltd. All rights reserved.