Introduction: What is Gene regulation?
Since the discovery of first example of gene regulation by François Jacob and Jacques Monod in 1961 in the form of lac operon, continuous efforts are being put in by various scientists for better understanding the mechanism underlying, how genes are regulated within cells. Gene regulation includes events that will allow cells to convert the message coded in DNA (genes) into gene products (Proteins or RNA). Gene regulation, is quite a complex process involving cross-talk between different proteins that will allow cells to know- when, in what tissues and for how long a particular gene or genes should be turned on and off. Hence, a fundamental understanding of gene regulation is critical to understanding how organisms develop and adapt to their environment and stress.

Regulation of genes drives the processes of cellular differentiation and morphogenesis, which is essential for the formation of different cell types in multicellular organism. In a multicellular organism different cell types exists and it is due to the events of gene regulation that they exhibit different gene expression profiles leading to variable cell types, though they all possess the same genome sequence.

As stated above eukaryotic DNA needs to be bound by various proteins for proper regulation of genes , so a description of the full set of proteins that regulate specific loci is critical to understanding
regulation. During the last two and half decades various chromatin strategies are employed to trace various proteins associated to particular loci. These strategies succeeded in enrichment of targeted region but none were able to give gave material of sufficient amount and purity to allow identification
of bound factors. Some other methods like yeast one hybrid and nucleic acid affinity capture,which connect specific DNA sequences to the proteins that directly associate with them were also developed. These methods were useful but did not provide complete protein composition at loci.

Then came Chromatin immunoprecipitation (ChIP) , a powerful technology to assess whether a protein of interest is bound to a given genomic region. One of the drawbacks of ChIP is that it relies on the use of antibodies and thus is limited to analysis of the factors that are tested and does not establish a complete description of composition.
In order to understand regulation better, Jérôme Déjardin and Robert E. Kingston to developed a strategy to purify an endogenous segment of chromatin in sufficient quantity and purity to identify the associated proteins. This protocol is named proteomics of isolated chromatin segments (PICh),uses a specific nucleic acid probe to isolate genomic DNA with its associated proteins in sufficient quantity and purity to allow identification of the bound proteins. In PIch cell will be fixed first , solubilizing of chromatin , then a specific probe will be hybridized to the chromatin, later the hybridized chromatin can be captured on magnetic beads, these hybrids can be eluted, and finally the
associated proteins can be identified by Mass spectrometry.

For more details on technique and advantages & disadvantages associated with PIch refer the resource papar by Jérôme Déjardin and Robert E. Kingston in this issue of Cell.

Reference:
Purification of Proteins Associated with Specific Genomic Loci
Jérôme Déjardin, Robert E. Kingston
DOI 10.1016/j.cell.2008.11.045

Image Credit: Jonas Hannestad / FlickR
Freakpower / FlickR

Related Articles