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The epigenetic inheritance of specific transcriptional states is commonly attributed to transitions in chromatin structure or changes in subnuclear localization. Kundu and Peterson (p. 2330-2340) exploit a budding yeast model for such transcriptional memory to evaluate the roles of the SWI/SNF chromatin remodeling enzyme, the H2A.Z histone variant, and gene tethering to the nuclear periphery. Surprisingly, they find no significant role for any of these nuclear processes but instead demonstrate that transcriptional memory in this system is controlled by the apparent cytoplasmic inheritance of signaling molecules.
The attachment of ubiquitin to specific lysine residues in substrates and ubiquitin during ubiquitination is important for generating diverse substrate-ubiquitin structures, providing versatility to this pathway in targeting proteins to different fates. The mechanism of lysine selection, however, remains poorly understood. Sadowski et al. (p. 2316-2329) show that the compatibility of amino acids adjacent to substrate or ubiquitin lysines with catalytic core residues of the ubiquitin-conjugating enzyme Cdc34 is critical for lysine selection and can specify if a substrate is mono- or polyubiquitinated. This new concept may be a general mechanism in directing the mode of ubiquitination in ubiquitin-conjugating enzymes.
Ephrins are important effectors of development and disease, yet the mechanisms by which their expression is regulated are largely unknown. Arvanitis et al. (p. 2508-2517) reveal that the expression of ephrin-B1 is controlled by a feedback mechanism involving posttranscriptional regulation via miR-124, a proneuronal miRNA. The authors describe a mutually repressive interaction between miR-124 and ephrin-B1 in neural progenitors and show that this mutual inhibition intercedes in neuronal differentiation. This work establishes that miRNAs are both mediators and regulators of ephrin signaling.