The human LIN28B nucleosome is inherently pre-positioned for efficient binding of multiple OCT4s without H3 K27 acetylation
Pioneer transcription factors possess the unique ability to access DNA within tightly packed chromatin structures, playing pivotal roles in cell differentiation and reprogramming. However, their precise mechanism for recognizing nucleosomes has remained mystery. Recent structural and biochemical investigations into the binding interactions between the human pioneer factor OCT4 and the LIN28B nucleosome by Sinha et al.1 and Guan et al.2 have yielded conflicting results regarding nucleosome positioning, nucleosomal DNA unwrapping, binding cooperativity, and the role of N-terminal tail of OCT4. In this study, we undertook a comparative analysis of these two research efforts and delved into the factors contributing to the observed discrepancies. Our investigation unveiled that the utilization of human and Xenopus laevis core histones, along with a discrete two-step salt dialysis method, led to distinct positioning of DNA within reconstituted LIN28B nucleosomes. Additionally, our reanalysis of the electrophoretic mobility shift assay data showed that H3 K27 acetylation did not increase OCT4 binding to the internal sites of the nucleosome when normalized to input; instead, it promoted sample aggregation. Thus, the available experimental data support the notion that the human LIN28B nucleosome is pre-positioned for efficient binding with multiple OCT4s, and there is no compelling evidence for its regulation by histone modifications.