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J. Biol. Chem., Vol. 279, Issue 51, 53160-53166, December 17, 2004

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In the Archaea Haloferax volcanii, Membrane Protein Biogenesis and Protein Synthesis Rates Are Affected by Decreased Ribosomal Binding to the Translocon^*

Gabriela Ring and Jerry Eichler

From the Department of Life Sciences, Ben Gurion University, Beersheva 84105, Israel

In the haloarchaea Haloferax volcanii, ribosomes are found in the cytoplasm and membrane-bound at similar levels. Transformation of H. volcanii to express chimeras of the translocon components SecY and SecE fused to a cellulose-binding domain substantially decreased ribosomal membrane binding, relative to non-transformed cells, likely due to steric hindrance by the cellulose-binding domain. Treatment of cells with the polypeptide synthesis terminator puromycin, with or without low salt washes previously shown to prevent in vitro ribosomal membrane binding in halophilic archaea, did not lead to release of translocon-bound ribosomes, indicating that ribosome release is not directly related to the translation status of a given ribosome. Release was, however, achieved during cell starvation or stationary growth, pointing at a regulated manner of ribosomal release in H. volcanii. Decreased ribosomal binding selectively affected membrane protein levels, suggesting that membrane insertion occurs co-translationally in Archaea. In the presence of chimera-incorporating sterically hindered translocons, the reduced ability of ribosomes to bind in the transformed cells modulated protein synthesis rates over time, suggesting that these cells manage to compensate for the reduction in ribosome binding. Possible strategies for this compensation, such as a shift to a post-translational mode of membrane protein insertion or maintained ribosomal membrane-binding, are discussed.

Received for publication, September 14, 2004 , and in revised form, October 7, 2004.

^* This work was supported by the Israel Science Foundation (Grant 433/03). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Dept. of Life Sciences, Ben Gurion University, P. O. Box 653, Beersheva 84105. Tel.: 972-8646-1343; Fax: 972-8647-9175; E-mail: jeichler{at}bgumail.bgu.ac.il.

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