Abstract

Gene specific targeting of the Sin3 corepressor complex by DNA-bound repressors is an important mechanism of gene silencing in eukaryotes. The Sin3 co-repressor is a scaffold protein able to interact with several proteins simultaniously. Sin3 specifically interacts with diverse transcriptional repressors, and was first identified as the MAD-family members.

Sin3 contains paired amphipatic helix repeat domains (PAH) which mediates protein-protein interactions, in addition Sin3 has a histone deacetylase binding site. The SID (Sin3 interacting domain), motif specifically interacts with the PAH2 domain in Sin3. In humans the Sin3 proteins has two spleicoforms; mSin3A and mSinB, both has the PAH2 domain and can interact with a SID containing protein.

The structure of the PAH2:MAD1 interaction has been solved (Brubaker et al., 2000). The SID helix is an amphiphatic alpha helix that engages in substancial hydrophobic interaction with a deep hydrophobic groove defined by two PAH2 helices.

Presumably all SID containing proteins are targeted to a DNA region either by direct DNA binding or interaction with a DNA binding partner, and recruit the Sin3-complex, which ultimatly leads to deacetylation and repression of transcription.

 Selected references

 This ELM has been assigned the following Gene Ontology (GO) terms for biological process, cellular component and molecular function.

Biological Process
development	GO:0007275
Cell growth and/or maintenance	GO:0008151
Cellular Component
nucleus	GO:0005634
Molecular Function
transcription regulator	GO:0030528