DNA-protein interactions are studied by using ChIP. The basic steps in this technique are crosslinking, sonication, immunoprecipitation, and analysis of the immunoprecipitated DNA. During ChIP, if chromatin is under-fragmented or fragments are too large which can lead to the increased background and lower resolution. Shorter cross-linking times (5-10 min) and/or lower formaldehyde concentrations (<1%) may improve shearing efficiency. If Chromatin is over-fragmented, then optimize shearing conditions for each cell type to improve ChIP efficiency. Over-sonication of chromatin may disrupt chromatin integrity and denature antibody epitopes. If you do not see any product or very little product in the input PCR reactions, add 5–10 μg chromatin per IP.
When extracting nucleic acids from cell cultures, thorough homogenization of cells via vortexing in lysis buffer is very necessary. Choose the best RNA isolation method keeping in mind the downstream applications, generally, column-based isolations result in clean and concentrated RNA samples. Downstream applications like sequencing and cDNA synthesis require high-quality RNA, always treat the samples with DNases and check their integrity by running a gel.
In ChIP, the most vital step is the binding of an antibody and choosing the right antibody. The binding affinity of different types of immunoglobulins to protein A or G differs significantly. Henceforth, it is recommended to choose either protein A or protein G coated beads. If you do not see any product in the positive control, add 5–10 μg of chromatin and 1–5 μg of antibody to each IP reaction and incubate with antibody overnight and an additional 2 hr after adding Protein G/A beads. If no product is observed in the experimental sample, add more DNA to the PCR reaction or increase the number of amplification cycles. Furthermore, if you have any problem with antibodies, make sure to use the ChIP-validated antibody.
In ChIP, the most vital step is the binding of an antibody and choosing the right antibody. The binding affinity of different types of immunoglobulins to protein A or G differs significantly. Henceforth, it is recommended to choose either protein A or protein G coated beads. If you do not see any product in the positive control, add 5–10 μg of chromatin and 1–5 μg of antibody to each IP reaction and incubate with antibody overnight and an additional 2 hr after adding Protein G/A beads. If no product is observed in the experimental sample, add more DNA to the PCR reaction or increase the number of amplification cycles. Furthermore, if you have any problem with antibodies, make sure to use the ChIP-validated antibody.
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