RNA polymerase II (RNAPII) is the enzyme transcribing most of the eukaryotic protein-coding genes. Analysing the distribution and quantification of RNAPII can help understanding its function in interphase nuclei. Although several investigations in mammals indicate the organization of RNAPII in so-called ‘transcription factories’ (Jackson et al., 1993; Rieder et al., 2012; Papantonis and Cook, 2013), their existence is still controversially discussed (Zhao et al., 2014).
Recently, based on super-resolution microscopy the presence of transcription factories was also suggested in plants. Applying structured illumination microscopy (SIM) and photoactivated localization microscopy (PALM) the distribution and number of RNAPII molecules in Arabidopsis nuclei was analysed and a positive correlation between RNAPII abundance and endopolyploidy was found (Schubert, 2014; Schubert and Weisshart, 2015).
Here, we present a protocol describing the isolation of Arabidopsis thaliana interphase nuclei via flow-sorting according to their endopolyploidy level, followed by a double immunostaining using antibodies specific for different RNAPII modifications and the subsequent evaluation by spatial SIM and PALM to achieve results regarding the abundance, distribution and co-localization of single inactive and active RNAPII molecules.
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