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Gpn1 and Gpn3 associate tightly and their protein levels are mutually dependent in mammalian cells
Lucía E Méndez-Hernández1, Ana E Pérez-Mejía1, Bárbara Lara-Chacón1
1Instituto de Física, Universidad Autónoma de San Luis Potosí, Manuel Nava 6, Zona Universitaria, C.P. 78290 San Luis Potosí, San Luis Potosí, Mexico.
Abstract:
Gpn1 and Gpn3 are GTPases individually required for nuclear targeting of RNA polymerase II. Here we show that whereas Gpn3-EYFP distributed between the cytoplasm and cell nucleus, it was mainly cytoplasmic when coexpressed with Gpn1-Flag. Gpn3-Flag retained Gpn1-EYFP in the cytoplasm. However, Gpn3-EYFP/Gpn1-Flag nucleocytoplasmic shuttling was revealed after inhibiting nuclear export with leptomycin B. All Gpn3-EYFP coimmunoprecipitated with Gpn1-Flag, and all Gpn1-EYFP with Gpn3-Flag. Importantly, most endogenous Gpn1 and Gpn3 also associate. Gpn1-Gpn3 interaction was essential to maintain steady-state protein levels of both GTPases. We propose that most Gpn1 and Gpn3 associate, are mobilized, and function as a protein complex.
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