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Different approaches are used for showing that Sds22 and Inhibitor-2 (I3) form a heterotrimeric complex with protein Ser/Thr phosphatase-1 (PP1). Cell lysates prepared under conditions that prevented the Sds22-induced inactivation of PP1 contained a catalytically inactive complex of Sds22, PP1 and I3, indicating that a pool of PP1 is complexly controlled by both Sds22 and I3.

The properties of the COOH-terminal domain of A-kinase anchoring protein 149 (AKAP149), which is found in mitochondria and in the endoplasmic reticulum-nuclear envelope network, are investigated. The results have shown that the KH-Tudor-containing domain of AKAP149 binds RNA in vitro and in RNA coprecipitation.

A-Kinase anchoring proteins (AKAPs) control the subcellular localization and temporal specificity of protein phosphorylation mediated by cAMP-dependent protein kinase. AKAP149 (AKAP1) is found in mitochondria and in the endoplasmic reticulum−nuclear envelope network where it anchors protein kinases, phosphatases, and a phosphodiesterase. AKAP149 harbors in its COOH-terminal part one KH and one Tudor domain, both known to be involved in RNA binding. We investigated the properties of the COOH-terminal domain of AKAP149. We show here that AKAP149 is a self-associating protein with RNA binding features. The KH domain of AKAP149 is sufficient for self-association in a RNA-dependent manner. The Tudor domain is not necessary for self-association, but it is required together with the KH domain for targeting to well-defined nuclear foci. These foci are spatially closely related to nucleolar subcompartments. We also show that the KH-Tudor-containing domain of AKAP149 binds RNA in vitro and in RNA coprecipitation experiments. AKAP149 emerges as a scaffolding protein involved in the integration of intracellular signals and possibly in RNA metabolism. [ABSTRACT FROM AUTHOR]