Transcription factors exert versatile molecular control of gene expression. Generally, transcription factors have both DNA binding domains and regulatory domains such as transactivation or signal sensing domains. The C. elegans bZip protein CEBP-1 is a conserved transcription factor required for multiple processes including synapse development, neuronal stress response, and axon regeneration. CEBP-1 consists of 319 amino acids with the C-terminal bZip domain homologous to the CCAAT/enhancer binding family, and N-terminal shows no clear homology by sequences. Here, we took advantage of genetic interaction screening and CRISPR genome editing to uncover a putative trans-activation domain of CEBP-1. We previously reported that loss of function of
cebp-1 fully suppresses the larval lethality in null animals of
nipi-3 (Kim et al, 2016), which encodes a conserved Tribbles pseudokinase and is required for animal development and innate immunity. We designed a highly efficient scheme to select for suppressor mutations of
nipi-3(0). We characterized a large number of mutations in
cebp-1. We found many mutations affecting the canonical DNA binding domain of CEBP-1. Unexpectedly, we identified several missense mutations clustered in the N-terminal region of CEBP-1, and these mutations behave similarly as genetic null of
cebp-1. To further explore the extent of the putative domain, we designed sgRNA-based targeted mutagenesis to this region. Our data reveal a stretch of 10-12 amino acids are absolutely essential for
cebp-1 function. C/EBP proteins in higher vertebrates also contain transactivation domains in the N-terminal region to modulate the activity of the DNA binding bZip domain. We are currently testing the hypothesis that this N-terminal domain may act as a transactivation domain. Kim, K. W., Thakur, N., Piggott, C. A., Omi, S., Polanowska, J., Jin, Y., & Pujol, N. (2016). Coordinated inhibition of C/EBP by Tribbles in multiple tissues is essential for Caenorhabditis elegans development. BMC biology, 14(1), 104.