hnRNP K Supports High-Amplitude D Site-Binding Protein mRNA ( mRNA) Oscillation To Sustain Circadian Rhythms.

Circadian gene expression is defined by the gene-specific phase and amplitude of daily oscillations in mRNA and protein levels. D site-binding protein mRNA ( mRNA) shows high-amplitude oscillation; however, the underlying mechanism remains elusive. Here, we demonstrate that heterogeneous nuclear ribonucleoprotein K (hnRNP K) is a key regulator that activates transcription via the poly(C) motif within its proximal promoter. Biochemical analyses identified hnRNP K as a specific protein that directly associates with the poly(C) motif Interestingly, we further confirmed the rhythmic binding of endogenous hnRNP K within the promoter through chromatin immunoprecipitation as well as the cycling expression of hnRNP K. Finally, knockdown of hnRNP K decreased mRNA oscillation in both and -dependent clock genes. Taken together, our results show rhythmic protein expression of hnRNP K and provide new insights into its function as a transcriptional amplifier of .