Abstract: A DNA fragment isolated from the DNA of T-even bacteriophage which suppresses the degradation of abnormal proteins in bacterial cells is disclosed. The DNA fragment can be isolated by treating the DNA of T-even bacteriophage with a restriction enzyme to cleave the DNA into fragments, at least one of said fragments consisting essentially of a sequence of nucleotide bases which code for protein that functions to suppress degradation of abnormal proteins in bacterial cells, inserting the DNA fragments into cloning vehicles, such as plasmids, to produce hybrid cloning vehicles, transforming bacterial cells by introducing the hybrid cloning vehicles therein, and selecting the transformants which exhibit suppressed protein degradation mechanisms. The DNA fragment can then be isolated from the selected transformants. The stabilizing DNA fragment can be introduced into bacterial host cells to increase the yield of foreign proteins expressed by cloned DNA.