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Fig. 3 | Epigenetics & Chromatin

Fig. 3

From: Functions of HP1 proteins in transcriptional regulation

Fig. 3

Assays typically used to determine if HP1 proteins are repressors or activators. There are three assays used most often to determine if a protein functions as a transcriptional activator or repressor: (1) Tethering studies, (2) position effect variegation (PEV) studies, and (3) expression studies in mutants. Tethering studies (left) use various methods (e.g. CRISPR/dCas9, LacI/LacO, etc.) to recruit a protein of interest to the promoter of a target reporter gene to observe if gene expression is increased, suggesting the protein is an activator of transcription, or decreased, suggesting the protein is a repressor. PEV studies (middle) utilize reporter genes with varying expression, shown here for the white gene in fly eyes and introduce a mutant allele for the protein of interest. If the protein of interest is a transcriptional repressor or functions in the maintenance of heterochromatin, a mutation will increase expression of the variegating reporter. If the protein of interest is a transcriptional activator or counteracts heterochromatin formation, a mutation will decrease expression of the variegating reporter. Gene expression studies in mutants (right) suggest that the protein functions as an activator is most genes are downregulated compared to wildtype, while if the protein functions as a repressor, most genes will be upregulated compared to wildtype

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