Threonylcarbamoyladenosine (t6A) is a universal modification found at position 37 of ANN decoding tRNAs, which imparts a unique structure to the anticodon loop enhancing its binding to ribosomes in vitro. Using a combination of bioinformatic, genetic, structural and biochemical approaches, the universal protein family YrdC/Sua5 (COG0009) was shown to be involved in the biosynthesis of this hypermodified base. Contradictory reports on the essentiality of both the yrdC wild-type gene of Escherichia coli and the SUA5 wild-type gene of Saccharomyces cerevisiae led us to reconstruct null alleles for both genes and prove that yrdC is essential in E. coli, whereas SUA5 is dispensable in yeast but results in severe growth phenotypes. Structural and biochemical analyses revealed that the E. coli YrdC protein binds ATP and preferentially binds RNAThr lacking only the t6A modification. This work lays the foundation for elucidating the function of a protein family found in every sequenced genome to date and understanding the role of t6A in vivo.

[structure: see text] Fermentation of ATCC 74256 led to the isolation and identification of C7 epimers of phomoidride A (CP-225,917) and phomoidride B (CP-263,114). We suggest the names phomoidrides C and D for these new fermentation products. Studies on the effect of pH on the distribution of phomoidrides A-D suggest phomoidride B (CP-263,114) is the first-formed secondary metabolite and the source of the remaining three phomoidrides.

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Doppeltes Spiel: Dimere Aminoglycosid‐Antibiotika wurden durch Verknüpfung von Neamin‐ oder Nebramin‐Kernen mit Linkern unterschiedlicher Länge und Zusammensetzung erhalten. Die Dimere zeigen hohe Affinität zum 16S‐A‐Zentrum ribosomaler RNA (siehe Schema) und wirken effektiv gegen mehrere aminoglycosidresistente Bakterienstämme.