Protein Methylation and Stress Granules: Posttranslational Remodeler or Innocent Bystander?

Figure 5

Stress granules contain symmetric dimethylarginine-containing proteins. HeLa cells were treated with 1.0 mM sodium arsenite for 20 minutes and subsequently immunostained with an antibody that detects the stress granule marker, TIA1 (red), and one that recognizes a subset of symmetrically dimethylarginine-containing proteins, SYM10 (green). The upper panel shows a confocal image of the stress granule containing cells. A magnified view of the boxed region is shown in the second set of panels. It is evident from the data that there are at least three types of granules that SYM10 recognize: large stress granules that colocalize with the TIA1 marker (yellow arrows), much smaller, non-colocalizing foci (green arrows), and a diffuse lattice or network (green circle). Colocalization analyses performed as described in Figure 2 clearly show that only the stress granules contain TIA1 and symmetrically dimethylated proteins. This was confirmed by subtracting the colocalized image from the green image; note the vacant black holes where the stress granules are. The graph quantifies the granule sizes of the colocalized and non-colocalized granules. The results were adapted from Dolzhanskaya et al. [27, Figure  14] and [20, Figure  12].