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The structure of tRNA guanine transglycosylase (TGT, gray surface and ribbon) from Zymomonas mobilis covalently linked to a stem-loop RNA substrate (green). TGT catalyzes the incorporation of a modified base in four tRNAs. The enzyme induces substantial conformation changes in the loop bases of the RNA substrate, and the structure of the covalent intermediate unambiguously identifies the aspartate residue that acts as the nucleophile for the reaction. See pages 781-788 and News and Views pages 772–773.
Recent studies of a tRNA guanine transglycosylase—a modifying enzyme known in all kingdoms of life—show how an unexpected active site aspartate becomes covalently attached to the tRNA substrate during catalysis, and how subsequent base exchange occurs in a single active site.
Four recent studies demonstrate that closing of a cleft in the myosin head is required for actin binding and nucleotide release. This represents a major breakthrough in understanding actomyosin-based motility.
The Hindu goddess Maha Devi is represented as having the power both to make and to destroy. Reminiscent of such power, two recent studies highlight the roles that nucleases play in both making and destroying RNAs associated with the mysterious world of small RNAs.
What prevents the replisome complex from moving along the DNA or breaking down when the replication fork stalls or encounters a DNA lesion? A recent paper describes how checkpoint proteins, Mrc1 and Tof1 couple the replisome to DNA synthesis.