Reviewer
Modesto Redrejo-Rodriguez
  • Assistant Professor, Biochemistry Department, Madrid Autonomous University
Research fields
  • Molecular Biology
Analysis of Direct Interaction between Viral DNA-binding Proteins by Protein Pull-down Co-immunoprecipitation Assay
Authors:  Ana Lechuga, Mónica Berjón-Otero, Margarita Salas and Modesto Redrejo-Rodríguez, date: 01/05/2018, view: 10286, Q&A: 0
This protocol analyzes the direct interaction between two DNA-binding proteins by pull-down co-immunoprecipitation. One of the proteins is overexpressed in E. coli as HA-tagged recombinant protein and cell-free extracts are immunoprecipitated in HA-affinity resin. Cell extracts are treated with nuclease to degrade DNA and RNA, which rules out nucleic acid-mediated indirect interaction. Then, a second immunoprecipitation step is performed using the purified putative partner protein. Co-immunoprecipitated proteins can be detected either by Coomassie Blue staining and/or Western blotting (WB) if a specific antibody is available. Moreover, many DNA/RNA binding proteins are highly electropositive, which can hinder WB under standard conditions, as has been shown in histones and histone-like proteins. In this case, we show that the high isoelectric point of the putative partner results in a poor transfer. Tips to troubleshot WB transfer of highly electropositive DNA-binding proteins are provided.
Determination of Mutation Frequency During Viral DNA Replication
This protocol is a simple method for evaluating mutation frequency during African swine fever virus (ASFV) replication, although it could be used also for other DNA viruses (poxvirus, herpesvirus, mimivirus, etc) with minor modifications. In the original Carrascosa et al. (1982), the protocol was carried out with two cloned viruses, BA71Vc (a purified clone from BA71V wild type strain) and vΔpolX (lacking the reparative polymerase, pol X, gene), and two different cell types that can be infected by ASFV, Vero cells and swine macrophages. To facilitate the sequence comparison, a genome fragment containing the B646L gene was amplified by PCR and blunt-end cloned. This gene codes for the major capsid protein (p72) and multiple sequences can be found in the database, so the mutations found could be compared with natural gene variations. The cloned fragment can be either sequenced directly from bacteria colonies or from miniprep purified DNA.
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