The ChIP (chromatin immuno-precipitation) assay is a powerful in vivo method used to quantify the interaction of a protein, such as a transcription factor, with specific DNA regions. This latest release from Promega, the HaloCHIP system, aims to increase the efficiency of such experiments by removing the need to generate specific antibodies that target the proteins in question. Traditional ChIP experiments make use of the fact that DNA-bound proteins can be cross-linked to the chromatin using formaldehyde fixation to ensure they stay bound to the DNA. This enables researchers to then lyse the cells and degrade the DNA before isolating the protein-DNA complexes using antibodies that specifically target the protein in question. The isolated DNA can then be identified using either PCR (polymerase chain reaction) techniques or DNA microarrays (ChIP-on-chip). One of the major disadvantages of the technique is the need to generate and validate such antibodies, a process that can considerably slow down such research. The new technique makes use of what the company has dubbed a HaloEnzyme that can be fused to a protein of interest and links the protein-DNA complex to a HaloLink resin to enable easy isolation. "The HaloCHIP System means that scientists no longer need to struggle to find the perfect antibody for their ChIP experiments," said Danette Hartzell, Promega R&D Scientist. The HaloEnzyme is linked to the protein of interest using cloning techniques in a 'HaloTag Vector' before the recombinant vector construct is transfected into cells. The proteins are then allowed bind to the DNA before formaldehyde cross-linking ensures the protein stays bound to the DNA while any non-specific protein-DNA complexes are washed away. The crosslinking is then reversed to release the DNA for analysis using either PCR or microarray analysis. In addition, because the HaloTag can be used to bind to other systems the same construct can be used in various other applications ranging from cellular imaging to protein-protein interaction analysis. "Since HaloCHIP is based on HaloTag Technology, researchers can easily run additional protein analysis applications, including cellular imaging and protein-protein interactions, using only one genetic construct. That yields both consistency and time savings," said Hartzell.