Abstract: The present invention provides an isolated nucleic acid comprising a first nucleotide sequence encoding an amino acid sequence comprising at least three positively charged amino acid residues, positioned upstream and in frame with a second nucleotide sequence encoding a protein. In addition, the present invention provides an isolated nucleic acid comprising a first nucleotide sequence encoding a DNA binding protein, positioned upstream and in frame with a second nucleotide sequence encoding a protein. An isolated nucleic acid is also provided, which comprises a first nucleotide sequence encoding a bacteriophage lambda repressor protein, positioned upstream and in frame with a second nucleotide sequence encoding a protein.