Figure 1.

pBSK-Zeo-5S-G5E4 (p5S) acceptor plasmids used in the work. The 2.56 kb 5S-G5E4 fragment DNA for polynucleosome assembly (PN) was previously described [62] and was cloned into the pBSP-zeo vector (A). This fragment is made of two times five repeats of 5S sequences surrounding a central sequence containing five gal4 DNA binding sites and the adenovirus 2 E4 minimal promoter. The p5S vector thus contains a region 1 containing nucleosome-positioning sequences and a region 2 containing the pBSK-zeo backbone. Each 5S fragment is separated by two EcoRI restriction sites. Nucleosome occupancy prediction performed using the method previously described by [53] and used in [36] indicates the formation on the chromatinized vector of two regions with different chromatin organization (regular and stable nucleosomes in the 5S-G5E4 region 1 and less organized and stable nucleosomes in the pBSK-Zeo backbone region 2 (B). Restriction inhibition assay demonstrates that the two regions are not equally accessible since region 1 is highly protected when chromatinized whereas region 2 remains highly accessible for restriction site cutting even in the nucleosomal structure (see Additional file 1: Figure S1).