IRAK1 and 4 interact with Pellino-1 (Jiang et al. 2003), 2 (Strellow et al. 2003) and 3 (Butler et al. 2005, 2007). Pellinos may act as scaffolding proteins, bringing signaling complexes into proximity. They are E3 ubiquitin ligases capable of ubiquitinating IRAK1, believed to mediate IL-1-stimulated formation of K63-polyubiquitinated IRAK1 in cells.
Though not clearly demonstrated and therefore not shown here, the current models of IRAK1 involvement suggest it would be within a complex including TRAF6.