ALKB-8 is a 2-oxoglutarate-dependent di-oxygenase homologous to bacterial AlkB, which oxidatively demethylates DNA substrates. The mammalian AlkB family contains AlkB homologues denominated ALKBH1 to 8 and FTO. The C. elegans genome
includes five AlkB-related genes, homologues of ALKBH1, 4, 6, 7, and 8, but lacks homologues of ALKBH2, 3, and 5 and FTO. ALKBH8 orthologues differ from other AlkB family members by possessing an additional methyltransferase module and an RNA binding N-terminal module. The ALKBH8 methyltransferase domain generates the wobble nucleoside 5-methoxycarbonylmethyluridine from its precursor 5-carboxymethyluridine and its (R)- and (S)-5-methoxycarbonylhydroxymethyluridine hydroxylated forms in tRNAArgUCG and tRNAGlyUCC. The ALKBH8/ALKB-8 methyltransferase domain is highly similar to yeast TRM9, which selectively modulates translation of mRNAs enriched with AGA and GAA codons under both normal and stress conditions. In this report, we studied the role of alkb-8 in C. elegans. We show that downregulation of alkb-8increases detection of lysosome-related organelles visualized by Nile red in vivo. Reversely, forced
expression of alkb-8 strongly decreases the detection of this compartment. In addition, overexpression of alkb-8 applied in a pulse during the L1 larval stage increases the C. elegans lifespan. and Corresponding author: Marta Kostrouchová
Mediator is a multiprotein complex that connects regulation mediated by transcription factors with RNA polymerase II transcriptional machinery and integrates signals from the cell regulatory cascades with gene expression. One of the Mediator subunits, Mediator complex subunit 28 (MED28), has a dual nuclear and cytoplasmic localization and function. In the nucleus, MED28 functions as part of Mediator and in the cytoplasm, it interacts with cytoskeletal proteins and is part of the regulatory
cascades including that of Grb2. MED28 thus has the potential to bring cytoplasmic regulatory interactions towards the centre of gene expression regulation. In this study, we identified MDT-28, the nematode orthologue of MED28, as a likely target of lysine acetylation using bioinformatic prediction of post-translational modifications. Lysine acetylation was experimentally confirmed using anti-acetyl lysine antibody on immunoprecipitated GFP::MDT-28 ex-pressed in synchronized C. elegans. Valproic acid (VPA), a known inhibitor of lysine deacetylases, enhanced the lysine acetylation of GFP::MDT-28. At the subcellular level, VPA decreased the nuclear localization of GFP::MDT-28 detected by fluorescence-lifetime imaging microscopy (FLIM). This indicates that the nuclear pool of MDT-28 is regulated by a mechanism sensitive to VPA and provides an indirect support for a variable relative proportion of MED28 orthologues with other Mediator subunits. and Corresponding author: Markéta Kostrouchová