Cover Story：Objective Pioneer transcription factors (PTFs) possess the unique ability to recognize and bind their target DNA sequences within compacted nucleosomal DNA, thereby initiating chromatin opening and gene expression. They play pivotal roles in fundamental biological processes such as embryonic development, cellular reprogramming, and tumorigenesis. The specific regulatory mechanism by which nucleosomal rotational positioning governs PTF-nucleosome interactions remains inadequately elucidated. This study aims to systematically investigate the role of the rotational orientation of motifs in PTF-nucleosome binding.Methods We employed a DNA deformation energy model to predict the rotational positioning of DNA on nucleosomes. We analyzed high-throughput in vitro data from the NCAP-SELEX assay, which profiles the binding landscapes of numerous transcription factors to nucleosomal DNA. For in vivo analysis, we integrated genome-wide binding data (ChIP-seq) and nucleosome positioning data (MNase-seq) for eight well-characterized pioneer factors (OCT4, SOX2, KLF4, GATA4, MYOD1, FOXA1, CEBPA, and ASCL1) in human cells. Binding motifs were classified as “TF-bound” if they overlapped with ChIP-seq peaks and “TF-unbound” otherwise. DNA bendability profiles and fast Fourier transform (FFT) analysis were used to assess rotational positioning patterns around these motif sites. This analytical framework was further applied to specific biological contexts, including cellular reprogramming from IMR90 fibroblasts to induced pluripotent stem cells (iPSCs) and the differentiation of human embryonic stem cells (hESCs) to human neuroectodermal cells (hNECs).Results Our in vitro analysis revealed a strong dependence of transcription factor binding on the rotational orientation of TF-binding motifs. For SOX7, the unbound motifs at specific enrichment peaks exhibited a rotational phase clearly opposite to that of the SOX7-bound motifs. Similarly, analysis of P53 binding sequences confirmed that successful binding in vitro correlated with model-predicted exposure of the DNA minor groove at the motif center, consistent with P53’s binding mode. Genome-wide in vivo analysis of the eight PTFs showed that their DNA binding motifs were generally associated with DNA sequences exhibiting significant 10-bp periodicity in bendability, suggesting an inherent potential for nucleosome association. Crucially, for most factors (except ASCL1), the average rotational positioning preferences were remarkably similar between TF-bound and TF-unbound motifs. This indicates that, at a global genomic level, rotational positioning is not the primary determinant dictating whether a nucleosomal motif is bound by its cognate PTF in vivo. This phenomenon persisted during cellular reprogramming (IMR90 to iPSC), where the rotational positioning of OSKM factor motifs bound versus unbound in nucleosomal regions showed no significant overall difference. Interestingly, during hESC differentiation to hNECs, SOX2 binding sites underwent comprehensive reprogramming. In hNECs, the rotational positioning of nucleosomal SOX2-bound motifs was significantly different and, unexpectedly, opposite to the general preference observed in hESCs and for unbound motifs in hNECs, suggesting a cell context-dependent rewiring of binding mechanisms.Conclusion This study suggests a distinction in the role of DNA rotational positioning in TF-nucleosome binding between in vitro and in vivo environments. While rotational positioning critically governs the binding efficiency of factors like SOX7 and P53 in simplified in vitro systems, PTFs in vivo appear to overcome this steric hindrance at the binding interface. The ability of PTFs to bind nucleosomal motifs, even when key interaction surfaces are partially buried, might stem from their unique structural properties (e.g., intrinsically disordered regions, DNA distortion/binding domains), nucleosome breathing which transiently exposes DNA, and potential cooperativity with other factors. Our results highlight the unique capacity of pioneer factors to drive chromatin openness through mechanisms beyond rotational positioning.