Figure 19.1: Vector map of episomal yeast plasmid Yep 24.

2. Integrating vector- Episomal yeast vectors are present as extra-chromosomal DNA and are unstable. This can over-come by integration of vector into the host chromosome. In yeast, integration occurs by homologous recombination. The yeast integration plasmids contain target sequence for integration into chromosomal DNA, a selection marker and bacterial origin of replication. Before vector delivery to the yeast, it is digested with the unique restriction endonuclease to produce linear DNA to increase the transformation efficiency and integration. In most of the cases integration is done in such a way that yeast chromosomal DNA remained intact and integration may not affect yeast growth. But in an alternate approach, a portion of yeast chromosomal DNA is replaced with the vector DNA through homologous recombination. These vectors are known as ‘ transplantment integration vector 'and they have foreign DNA, selection marker and homologous DNA to the region of chromosomal DNA to be replaced.