Eukaryotic genomes are compacted in the nucleus as chromatin, an array of nucleosomes (~147 bp of DNA wrapped around a histone octamer) connected by short linker DNA segments. This bead-on-string structure restricts access to DNA sequences, modulating all nuclear processes, including transcription. In eukaryotes, transcription is catalysed by RNA polymerase II (Pol II). Nucleosomes stand a major energy barrier to Pol II progression, which is associated to partial disassembly and displacements of the particle. Despite many structural studies in vitro, the interplay between chromatin organization and transcription is poorly understood, especially in situ where the local chromatin architecture during transcription is unknown. We have recently demonstrated the potential of cryo electron tomography (cryo-ET) to resolve nucleosome and chromatin folding in situ, unveiling their structural heterogeneity in relationship with their functional compartmentalization. We will explore how transcription couples to local chromatin organisation, assembly and disassembly in situ. This experimental internship in the field of structural biology includes complete cryo-ET workflow from sample preparation to cryo-tomogram acquisition on high end instruments. It will also include first data analyses: tomogram reconstruction & denoising, particle picking & segmentation, sub-tomogram averaging. We dispose of a large set of preliminary data for training and test of data analysis tools.