MicroRNA Processing: Battle of the Bulge Blake C. Meyers, Stacey A. Simon, Jixian Zhai  Current Biology  Volume 20, Issue 2, Pages R68-R70 (January 2010) DOI: 10.1016/j.cub.2009.12.008 Copyright © 2010 Elsevier Ltd Terms and Conditions

Figure 1 Model of the influence of secondary structure on plant pri-miRNA processing. A generalized model of plant pri-miRNA structures. Song et al. [1] devised the ‘+15 rule’, for which the first DCL1 cleavage occurs ∼15 nt from either the end of the hairpin or a less-structured region with greater than two consecutive unpaired nucleotides. Loss of bulges within the 15-nt region may improve pri-miRNA processing. Relocating this loop can shift the initial cleavage site [2]. The region below the stem-loop may or may not be single-stranded RNA (ssRNA). The size of the upper loop in plant pri-miRNAs is highly variable. Red arrowheads indicate the site of the first Dicer cleavage event, purple the second. Depending on the miRNA, the miRNA–miRNA∗ duplex may be on either the 5′ or 3′ arm of the MIR precursor hairpin. Current Biology 2010 20, R68-R70DOI: (10.1016/j.cub.2009.12.008) Copyright © 2010 Elsevier Ltd Terms and Conditions