Apg16p mediates Apg5p assembly. Immunoprecipitation was carried out as described in Figure 3, using apg12Δ (YNM107) and apg12Δapg16Δ cells (YNM115) carrying pMyc‐APG12 (CEN) and pHA‐APG12 (CEN) (A), or pMyc‐APG12 (CEN) and pHA‐APG5 (CEN) (B). Following SDS-PAGE, immunoprecipitates were subjected to immunoblot analysis using anti‐HA or anti‐Myc antibody as indicated. A model of the Apg12p-Apg5p-Apg16p complex is illustrated in each panel. Apg16p forms a homo‐oligomer through its C‐terminal coiled‐coil region. It is not clear whether Apg16p forms a dimer or a larger multimer. The N‐terminal region of each Apg16p interacts with Apg5p; most of these complexes are conjugated to Apg12p (A) but a small population are unmodified (B). In the absence of Apg16p, separate Apg5ps do not assemble. 