5-5.7.2. Insertion sites

• Plastid expression vectors possess left and right flanking sequences each with 1–2 kb in size from the host plastid genome, which facilitates foreign gene insertion into plastid DNA via homologous recombination.
  
  
• The insertion site in the plastid genome is determined by the choice of plastid DNA segment flanking the marker gene and the gene of interest. The foreign DNA is inserted in intergenic regions of the plastid genome.
  
  
• Most commonly used insertion sites are trnV-3'rps12，trnI-trnA and trnfM-trnG.
  
  

The trnV-3'rps12 and trnI-trnA sites are located in the 25 kb inverted repeat (IR) region of plastid DNA and insertion of gene into these sites results in the rapid copying into two copies in the IR region.
The trnfM-trnG site is located in the large single copy region of the plastid DNA. The insertion of gene between trnfM and trnG should contain only one copy per plastid DNA. pSBL- CTV2 was the first vector developed in the Daniell laboratory for expression of several proteins. This vector inserts the foreign gene in trnI-trnA intergenic region.