To identify interaction partners of POC1B in the retina, we employed a GAL4-based interaction trap screen in yeast (yeast two-hybrid system). We screened a library expressing human retinal cDNAs for potential interactors of POC1B. Both a construct expressing full-length POC1B and constructs expressing different POC1B fragments were used as baits (Figure S1). The fragment containing the carboxy-terminal coiled-coil domain of POC1B was found to putatively interact with five different proteins, including FAM161A (Figure S5A). The interaction with this known retinal-disease-associated protein21,27,28 caught our attention and was confirmed by a coimmunoprecipitation assay using both full-length proteins (Figure 5A). In the same assay, we investigated the effect of the identified missense and single-amino-acid deletion variants in POC1B on the interaction. Indeed, a significantly lower amount of altered POC1B than wild-type protein coprecipitated with FAM161A, indicating a disrupted physical interaction. The unrelated p63 did not coprecipitate with either POC1B or FAM161A, which confirmed specificity of the interaction between POC1B and FAM161A in the coimmunoprecipitation assay. The interaction between wild-type POC1B and FAM161A, and the decreased interaction between variant POC1B proteins and FAM161A, was confirmed by reciprocal coimmunoprecipitation (Figure S5B). Uncropped images of the immunoblots are shown in Figure S6.