Initiation of protein synthesis in bacteria at a translational start codon of mammalian cDNA: Effects of the preceding nucleotide sequence

Plasmids containing a mouse cDNA sequence encoding the enzyme dihydrofolate reductase (DHFR; tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate:NADP⁺ oxidoreductase, EC 1.5.1.3) have been used to study the efficiency of initiation of protein synthesis at an ATG (AUG) translational start codon indigenous to the eukaryotic cDNA. Differences in DHFR production assayed phenotypically, enzymatically, and immunologically were correlated with the primary structure of the DNA segment that precedes the translational start codon. Our results indicate that initiation of a structurally discrete and biologically functional eukaryotic protein can occur in bacteria on a fused mRNA molecule, and that the efficiency of expression is strongly affected by: the extent of homology of the translational control region with the 3'-OH end of 16S ribosomal RNA, and the distance between the protein start codon and the ribosome-binding sequence on the mRNA.