Featured System - July 2008
Short description: Living cells are filled with RNases, but not highly destructive ones like our digestive RNase.
Living cells are filled with RNases, but not highly destructive ones like our digestive RNase. Instead, our cellular RNases are specific and perform specialized tasks. Many of these choreograph the timely degradation of messenger RNA strands after they have finished their jobs. Other RNases play essential roles in the synthesis of more permanent forms of RNA, such as transfer RNA and ribosomal RNA. Many RNA molecules are built as long precursors, which are then trimmed to the final functional length. In Escherichia coli, RNase T has the job of performing the last cut in transfer RNA production, forming the proper CCA 3' end that is used to carry amino acids. It also performs the final trimming in the 5S and 23S ribosomal RNA molecules, which have a CC sequence at their 3' ends. In other organisms, the process is not quite this simple, since some transfer RNA molecules are not synthesized with their CCA sequence built in. In those cases, other RNases clip the strand, and a dedicated enzyme (tRNA nucleotidyl transferase) builds a new CCA on the exposed end.
T-Rex can distinguish the small chemical difference between NAD+ and NADH. In this Jmol image, two NADH molecules are in spacefilling spheres. The nicotinamide rings are close together at the center with a phenylalanine (in turquoise) bound in between. The nicotinamides are surrounded by hydrophobic amino acids, including a key tyrosine (in magenta) that interacts with the nicotinamide carbon atom that is reduced. Notice that the binding site is asymmetric, with one of the phenylalanines bound b
Y. Zuo, H. Zheng, Y. Wang, M. Chruszcz, M. Cymborowski, T. Skarina, A. Savchenko, A. Malhotra and W. Minor (2007) Crystal structure of Rnase T, and exoribonuclease involved in tRNA maturation and end turnover. Structure 15, 417-428.
Y. Zuo and M. P. Deutscher (2002) The physiological role of Rnase T can be explained by its unusual substrate specificity. Journal of Biological Chemistry 277, 29654-29661.