B23 interacts with PES1 and is involved in nucleolar localization of PES1.

PES1, the human homolog of zebrafish pescadillo, is a nucleolar protein that is essential for cell proliferation. We report herein that a nucleolar marker protein B23 physically interacts with PES1 and is involved in the nucleolar localization of PES1. In vivo interaction between B23 and PES1 was verified by co-immunoprecipitation of endogenous B23 and PES1 proteins, and they showed cellular co-localizations under both normal and actinomycin D-induced stress conditions. Furthermore, we mapped their interaction domains via in vitro pulldown assays. When B23 was knocked down by RNA interference, there appeared an increased nucleoplasmic distribution of PES1. Our results support a previous hypothesis that B23 might be a nucleolar hub protein for protein targeting to the nucleolus, and shed light on the nucleolar localization mechanism of PES1. The physical interaction between B23 and PES1 implies that they may participate in ribosome biogenesis in a protein complex.