Prompt Description

The preparation of recombinant human insulin begins with the design and synthesis of the human insulin gene. Human insulin consists of two peptide chains, A and B; therefore, two synthetic genes are typically designed: one encoding the A chain and one encoding the B chain. Researchers optimize *E. coli*-preferred codons based on the natural insulin amino acid sequence and chemically synthesize these two gene segments. Then, restriction enzymes are used to insert the A-chain or B-chain gene into a vector plasmid, constructing a recombinant expression plasmid. The plasmid also needs to contain functional elements such as promoters and terminators, and antibiotic resistance markers to achieve efficient gene transcription and selection. Commonly used expression vectors generally carry strong promoters (such as T7 or tryptophan promoters) and RBS to drive high-level expression of the inserted gene in the host bacteria. Here, the A and B genes are cloned separately into circular plasmids. As shown in the illustration, the proinsulin gene (containing A and B chain sequences) is extracted from the cell nucleus in the upper left; the circular plasmid opened with restriction enzymes is in the upper right, and the vector contains a promoter and resistance gene. After the enzymatic reaction, the A-chain gene and the B-chain gene are ligated into different sites on the plasmid, forming a recombinant plasmid for downstream expression.