ACKNOWLEDGEMENTS
We thank Niilo Kaldalu and Arto Pulk (University of Tartu) for their helpful discussions and help writing the manuscript. Furthermore, we thank Dr Hirotada Mori (Nara Institute of Science and Technology, Japan) for sending us the TransBac plasmid library. Finally, we thank Aksel Soosaar and Viia Kõiv (University of Tartu) for their technical advice and support. This work was supported by funds from the European Regional Development Fund through the Centre of Excellence for Molecular Cell Technology and the Estonian Research Council (grant PRG335).