Allelic forms of DRG1/AFG2 confer resistance to the drug diazaborine, an inhibitor of ribosome biogenesis in Saccharomyces cerevisiae. Our results show that the AAA-ATPase Drg1 is essential for 60S maturation and associates with 60S precursor particles in the cytoplasm. Functional inactivation of Drg1 leads to an increased cytoplasmic localization of shuttling pre-60S maturation factors like Rlp24, Arx1, and Tif6. Surprisingly, Nog1, a nuclear pre-60S factor, was also relocalized to the cytoplasm under these conditions, suggesting that it is a previously unsuspected shuttling preribosomal factor that is exported with the precursor particles and very rapidly reimported. Proteins that became cytoplasmic under drg1 mutant conditions were blocked on pre-60S particles at a step that precedes the association of Rei1, a later-acting preribosomal factor. A similar cytoplasmic accumulation of Nog1 and Rlp24 in pre-60S-bound form could be seen after overexpression of a dominant-negative Drg1 variant mutated in the D2 ATPase domain. We conclude that the ATPase activity of Drg1 is required for the release of shuttling proteins from the pre-60S particles shortly after their nuclear export. This early cytoplasmic release reaction defines a novel step in eukaryotic ribosome maturation.Biogenesis of the ribosomal subunits in Saccharomyces cerevisiae starts with transcription of the 35S pre-rRNA, which is a common precursor for the individual rRNAs for both the small and large ribosomal subunits. This pre-rRNA assembles with ribosomal and nonribosomal proteins to form a 90S preribosomal particle (for recent reviews on ribosome biogenesis, see references 5, 6, and 32). During maturation, preribosomal particles undergo substantial changes in protein composition, which are accompanied by a series of pre-rRNA processing events (see reference 5). Separation of the biogenesis pathways for the 40S and 60S subunits occurs when the 32S precursor rRNA is cleaved into the 20S and 27SA2 pre-rRNAs, the precursors for the small-and large-subunit rRNAs, respectively.

A novel biocatalytic protocol for CC bond formation is described and is an equivalent to Friedel–Crafts alkylation. S‐Adenosyl‐L‐methionine (SAM), the major methyl donor for biological methylation catalyzed by methyltransferases (Mtases), can perform alkylations (see scheme). These enzymes can accept non‐natural cofactors and transfer functionalities other than methyl onto aromatic substrates.

Eine neuartige biokatalytische C‐C‐Verknüpfung, die äquivalent zur Friedel‐Crafts‐Alkylierung ist, wird vorgestellt. S‐Adenosyl‐L‐methionin (SAM), der Haupt‐Methyldonor bei Methyltransferase(Mtase)‐katalysierten biologischen Methylierungen, kann Alkylierungen bewirken (siehe Schema). Diese Enzyme akzeptieren nichtnatürliche Cofaktoren und können andere Funktionalitäten als Me auf aromatische Substrate übertragen.