bioRxiv preprint doi: https://doi.org/10.1101/204743; this version posted December 12, 2017. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. Strong binding activity of few transcription factors is a major determinant of open chromatin Bei Wei1, Arttu Jolma1, Biswajyoti Sahu2, Lukas M. Orre3, Fan Zhong1, Fangjie Zhu1, Teemu Kivioja2, Inderpreet Kaur Sur1, Janne Lehtiö3, Minna Taipale1 and Jussi Taipale1,2,4* 1Division of Functional Genomics and Systems Biology, Department of Medical Biochemistry and Biophysics, and Department of Biosciences and Nutrition, Karolinska Institutet, SE 141 83, Stockholm, Sweden 2Genome-Scale Biology Program, P.O. Box 63, FI-00014 University of Helsinki, Finland 3Department of Oncology-Pathology, Science for Life Laboratory, Karolinska Institutet, SE 141 83, Stockholm, Sweden 4Department of Biochemistry, University of Cambridge, United Kingdom *To whom correspondence should be addressed. E-mail:
[email protected] Abstract It is well established that transcription factors (TFs) play crucial roles in determining cell identity, and that a large fraction of all TFs are expressed in most cell types. In order to globally characterize activities of TFs in cells, we have developed a novel massively parallel protein activity assay, Active TF Identification (ATI) that measures DNA-binding activity of all TFs from any species or tissue type. In contrast to previous studies based on mRNA expression or protein abundance, we found that a set of TFs binding to only around ten distinct motifs display strong DNA-binding activity in any given cell or tissue type.