[The antidiphtheria activity of the pre-EGF fragment]

The DNA fragment, coding a part of the protein molecule--the precursor of the epidermal growth factor (pre-EGF76-208)--and containing the sequence of 133 N-end amino acid residues, was obtained with the use of gene engineering and molecular biological techniques. For this purpose a fraction of poly(A+) = RNA was isolated from the kidney of a newborn infant; on this fraction the "library" of cDNA fragments whose coding capacity corresponded to the required sequence of mRNA in the pre-EGF gene was obtained in the reaction of reverse transcription, conjugated with the polymerase chain reaction (PCR). After the determination of the nucleotide sequences in 11 fragments only 1 fragment which contained practically no mutations appearing in PCR as the result of amplifications was chosen. This fragment was used for the construction of a hybrid plasmid controlling the synthesis of hybrid fusion protein with the sequence of pre-EGF76-208. Fusion protein was synthesized with very low effectiveness, but the use of metallo-affinity chromatography permitted to isolate and purify it, its purity reaching 98%. Then its antitoxic activity was determined in the skin test on guinea pigs and found to be not less then 10(6) I.U./mg of protein.