Pri-microRNA processing is necessary to form maturated microRNA (miRNA), an integral class of RNAs responsible for regulating genes that control a wide variety of developmental processes as well as apoptosis and hematopoiesis. Drosha, a class 2 RNase enzyme, and its partner known as the Di George Critical Region 8 protein (DGCR8, also know as Pasha in insects and worms) together form what is termed as the microprocessor complex, a protein-protein complex which processes microRNAs. DGCR8 and Drosha are responsible for the maturation of primary transcripts of miRNAs (pri-miRNAs) into precursor miRNAs (pre- miRNAs) in the first step of the miRNA maturation pathway in animals. Intriguingly, the dimeric form of DGCR8 was recently discovered to associate with heme when overexpressed in E. coli. Using spectroscopic methods such as electronic absorption, magnetic circular dichroism (MCD), electron paramagnetic resonance (EPR) and resonance Raman (rR), we have shown that the heme in DGCR8 associates with the dimer using two cysteine amino acid side chains. This discovery was the first of its kind to show that Cys/Cys is a naturally occurring heme-ligation motif. However, the method by which heme regulates miRNA processing is currently unknown and is under investigation in collaboration with Dr. Feng Guo and his research lab at the University of California, Los Angeles.

DGCR8 EPR Spectra

Electronic absorption, MCD and EPR spectroscopies were used to characterize the DGCR8-heme interaction as the first of its kind to use a Cys/Cys Fe(III) ligation motif. The function of how heme may regulate miRNA processing is still unknown.