Abstract: Restriction enzymes are used to remove from DNA a complete and undamaged structural gene coding region for the expression of DNA polymerase I (polA) without the gene's natural promoter or with only a significantly damaged portion of the gene's natural promoter. Also by the use of restriction enzymes, a segment from a plasmid cloning vector is excised at a position adjacent to a promoter which is conditionally controllable and may be more powerful than the damaged or removed promoter. The gene for DNA polymerase I is enzymatically cloned into said vector at the position of said removed segment and adjacent to said conditionally controllable promoter. Multicopies of the cloned vector are introduced into a host baterial strain (E. coli). The host strain is then cultured so that the cell colony grows and replicates new generations containing replicated foreign plasmid. During such said replication the activity of said controllable promoter is repressed.

Abstract: Restriction enzymes are used to remove from DNA a complete and undamaged structural gene coding region for the expression of DNA polymerase I (polA) without the gene's natural promoter or with only a significantly damaged portion of the gene's natural promoter. Also by the use of restriction enzymes, a segment from a plasmid cloning vector is excised at a position adjacent to a promoter which is conditionally controllable and may be more powerful than the damaged or removed promoter. The gene for DNA polymerase I is enzymatically cloned into said vector at the position of said removed segment and adjacent to said conditionally controllable promoter. Multicopies of the cloned vector are introduced into a host baterial strain (E. coli). The host strain is then cultured so that the cell colony grows and replicates new generations containing replicated foreign plasmid. During such said replication the activity of said controllable promoter is repressed.

Abstract: Restriction enzymes are used to remove from DNA a complete and undamaged structural gene coding region for the expression of DNA polymerase I (polA) without the gene's natural promoter or with only a significantly damaged portion of the gene's natural promoter. Also by the use of restriction enzymes, a segment from a plasmid cloning vector is excised at a position adjacent to a promoter which is conditionally controllable and may be more powerful than the damaged or removed promoter. The gene for DNA polymerase I is enzymatically cloned into said vector at the position of said removed segment and adjacent to said conditionally controllable promoter. Multicopies of the cloned vector are introduced into a host baterial strain (E. coli). The host strain is then cultured so that the cell colony grows and replicates new generations containing replicated foreign plasmid. During such said replication the activity of said controllable promoter is repressed.