Internal-loops (also termed interior loops) in RNA are found where the double stranded RNA separates due to no Watson-Crick-Franklin base pairing between the nucleotides. Internal-loops differ from Stem-loops as they occur in middle of a stretch of double stranded RNA. The non-canonicoal residues result in the double helix becoming distorted due to unwinding, unstacking and kinking.
Internal-loops can be classified as either symmetrical or asymmetrical, with some asymmetrical internal-loops, also known as bulges. Many important structural motifs are composed of internal loops such as
the C-loop,[1]
the docking-elbow,[2]
kink-turns (k-turn),[3][4]
the right-angle,[5]
the sarcin/ricin loops (also called bulged-G motifs),[6][7][8]
the twist-up motif[9]
and the UAA/GAN internal loop motif.[10]
^Leontis, NB; Westhof, E (Oct 30, 1998). "A common motif organizes the structure of multi-helix loops in 16 S and 23 S ribosomal RNAs". Journal of Molecular Biology. 283 (3): 571–83. doi:10.1006/jmbi.1998.2106. PMID9784367.
^ abLee, JC; Gutell, RR; Russell, R (Jul 28, 2006). "The UAA/GAN internal loop motif: a new RNA structural element that forms a cross-strand AAA stack and long-range tertiary interactions". Journal of Molecular Biology. 360 (5): 978–88. doi:10.1016/j.jmb.2006.05.066. PMID16828489.