SID-4/NCK-1 is important for dsRNA import in Caenorhabditis elegans

RNA interference (RNAi) is sequence-specific gene silencing triggered by double-stranded (ds)RNA. When dsRNA is expressed or introduced into one cell and is transported to and initiates RNAi in other cells, it is called systemic RNAi. Systemic RNAi is very efficient in C. elegans and genetic screens for systemic RNAi defective (Sid) mutants have identified RNA transporters (SID-1, SID-2 and SID-5) and a signaling protein (SID-3). Here we report that SID-4 is nck-1, a C. elegans NCK-like adaptor protein. sid-4 null mutations cause a weak, dosesensitive, systemic RNAi defect and can be effectively rescued by SID-4 expression in target tissues only, implying a role in dsRNA import. SID-4 and SID-3 (ACK-1 kinase) homologs interact in mammals and insects, suggesting they may function in a common signaling pathway, however, a sid-3; sid-4 double mutants showed additive resistance to RNAi, suggesting that these proteins likely interact with other signaling pathways as well. A bioinformatic screen coupled to RNAi sensitivity tests identified 23 additional signaling components with weak RNAi defective phenotypes. These observations suggest that environmental conditions may modulate systemic RNAi efficacy, and indeed, sid-3 and sid-4 are required for growth temperature effects on systemic RNAi silencing efficiency.

Resistivity of plutonium, neptunium and uranium due to the accumulation of radioactive self damage

An increase with time in resistivity occurs in plutonium at low temperatures as a result of radioactive self damage. The effect has been studied in experiments at liquid helium temperature lasting over 8000h and has been found to exist in the α , β and δ phases of the metal. In all cases the resistivity approaches saturation, the rates of increase depending on the crystal structure and isotropic content of the sample. In spite of wide differences in these rates the functional increase is roughly the same. The temperature dependence of the accumulated resistivities in all three modifications deviates very strongly from a simple additive resistance obeying Matthiesen’s rule. The resistivity of fully damaged α plutonium is almost temperature independent, becoming smaller than that of the undamaged specimen above about 50 °K. Measurements on neptunium and uranium 233 have also shown resistivity increases with time at helium temperatures, but the effect is too small to decide whether Matthiesen’s rule is obeyed in these metals. The observed effects have been discussed under the assumption that in plutonium scattering of electrons at low temperatures is mainly due to a co-operative phenomenon.