In today’s new issue of JCB, He et al. describe how the scaffold proteins ankyrin-G and βII-spectrin are targeted to the lateral membrane of columnar epithelial cells in order to promote lateral membrane assembly. As described in this week’s In Focus, the palmitoyltransferases DHHC5 and DHHC8 target ankyrin-G by palmitoylating the protein’s N-terminal region. βII-spectrin, in turn, associates with ankyrin-G but must also bind to phosphoinositides in order to localize specifically at the lateral membrane.
Chen et al. reveal how cells coordinate their response to starvation so that they don’t degrade their components unnecessarily. Under mild starvation conditions, the general amino acid control pathway upregulates the expression of amino acid transporters that import free amino acids into the cell. These amino acids then reactivate the mTOR kinase to suppress the autophagy pathway that would otherwise send cellular contents to the lysosomes to be degraded and recycled. More here.
Zeman et al. describe how cells regulate the ubiquitin ligase Rad18 in order to fine-tune their response to specific types of DNA damage. As explained here, ubiquitination inhibits Rad18’s activity in undamaged cells, but this posttranslational modification is quickly removed in response to the DNA-alkylating agent MMS or H2O2, allowing Rad18 to activate the specific downstream pathway that helps the cell’s replication machinery tolerate the damage and suppress mutagenesis.
And Cain et al. reveal that the LINC complexes that span the nuclear envelope do not maintain the space between nuclear membranes, except in cells exposed to mechanical stress. The complexes, which consist of inner nuclear membrane SUN proteins and outer nuclear membrane KASH proteins, have a variety of functions but C. elegans lacking the somatic SUN protein UNC-84 have a normally-sized perinuclear space in most cell types. But larger gaps appear between the inner and outer nuclear membranes in body wall muscle cells. More here.
And three papers from today’s new issue are discussed in this month’s biobytes podcast. Usha Acharya describes her lab’s finding that a sirtuin deacetylase regulates mitochondrial ATP synthesis (Rahman et al.). And the authors of two papers (Elting et al. and Sikirzhytski et al.) discuss their complementary results demonstrating that the motor protein dynein binds to the minus ends of spindle microtubules and helps to maintain spindle architecture and segregate chromosomes in the absence of direct connections between chromosome kinetochores and spindle poles. You can listen below or subscribe in iTunes.
That’s all for today, but you can find the journal’s full table of contents here.
Cover image showing the appearance of a large gap between the inner and outer nuclear membranes of a C. elegans body wall muscle cell lacking UNC-84 © 2014 Cain et al.