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. Author manuscript; available in PMC: 2011 Oct 13.
Published in final edited form as: Nat Rev Genet. 2011 Aug 18;12(9):615–627. doi: 10.1038/nrg3030

Figure 2. Mechanisms that position integration.

Figure 2

A. The Ty3 targeting mechanism: Integration of Ty3 occurs one or two bp upstream of tRNA genes. This pattern requires Brf1 and TBP, components of TFIIIB that recruit integrase (IN, gray oval) to the target site. B. The Ty1 targeting mechanism: The factor Bdp1 is a component of TFIIIB (green circles) that is required to recruit the chromatin remodeling complex Isw2 (light blue semi-circle). Integration of Ty1 occurs with an 80 bp periodicity in a 700 bp window upstream of tRNA genes. The periodicity requires both Bdp1 and Isw2. C. The mechanism of Tf1 targeting: Tf1 integrates into promoters transcribed by RNA polymerase II. Transcription factors (Act), such as Atf1p, bind to the promoter and recruit IN to the insertion sites. D. The mechanism of Ty5 integration: In the absence of a stress condition, the phosphorylation of the IN targeting domain (blue knob on TD) directs integration to heterochromatin by binding a structural component of the heterochromatin, Sir4 (green ovals). Orange cylinders indicated condensed nucleosomes; black lines represent DNA. When cells are exposed to environmental stress the IN is dephosphorylated and integration occurs in gene rich regions.