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| Subject Categories: Membranes & Transport | Plant Biology |
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| The EMBO Journal
(2003) 22, 807–815, doi:10.1093/emboj/cdg081 |
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Thylakoid targeting of Tat passenger proteins shows no  pH dependence in vivo |
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| Giovanni Finazzi2, Claudia Chasen1, Francis-André Wollman1 and Catherine de Vitry1 |
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1 Physiologie Membranaire et Moléculaire du Chloroplaste CNRS UPR1261, Institut de Biologie Physico-Chimique, 13 Rue Pierre et Marie Curie, 75005 Paris, France 2 Istituto di Biofisica del CNR, Milan, Italy To whom correspondence should be addressed Francis-André Wollman, wollman@ibpc.fr Received 14 August 2002; Revised 25 November 2002; Accepted 16 December 2002. |
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| Abstract |
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| The Tat pathway is a major route for protein export in prokaryotes and for protein targeting to thylakoids in chloroplasts. Based on in vitro studies, protein translocation through this pathway is thought to be strictly dependent on a transmembrane pH. In this paper, we assess the pH sensitivity of the Tat pathway in vivo. Using Chlamydomonas reinhardtii, we observed changes in the efficiency of thylakoid targeting in vivo by mutating the Tat signal of the Rieske protein. We then employed two endogenous pH probes located on the lumen side of the thylakoid membranes to estimate spectroscopically the pH in vivo. Using experimental conditions in which the trans-thylakoid pH was almost zero, we found no evidence for a pH dependence of the Tat pathway in vivo. We confirmed this observation in higher plants using attached barley leaves. We conclude that the Tat pathway does not require a pH under physiological conditions, but becomes pH sensitive when probed in vitro/in organello because of the loss of some critical intracellular factors. |
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| Keywords: chloroplast, pH, protein import, Rieske protein, Tat pathway |
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