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J. Biol. Chem., Vol. 281, Issue 34, 24728-24736, August 25, 2006

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Androcam Is a Tissue-specific Light Chain for Myosin VI in the Drosophila Testis^*

Deborah J. Frank¹², Stephen R. Martin¹, Bridget N. T. Gruender, Yung-Sheng R. Lee^¶, Rebecca A. Simonette^¶, Peter M. Bayley, Kathryn G. Miller, and Kathleen M. Beckingham^¶3

From the Department of Biology, Washington University, St. Louis, Missouri 63130, the Division of Physical Biochemistry, National Institute for Medical Research, Mill Hill, London, NW7 1AA, United Kingdom, and the ^¶Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005

Myosin VI, a ubiquitously expressed unconventional myosin, has roles in a broad array of biological processes. Unusual for this motor family, myosin VI moves toward the minus (pointed) end of actin filaments. Myosin VI has two light chain binding sites that can both bind calmodulin (CaM). However unconventional myosins could use tissue-specific light chains to modify their activity. In the Drosophila testis, myosin VI is important for maintenance of moving actin structures, called actin cones, which mediate spermatid individualization. A CaM-related protein, Androcam (Acam), is abundantly expressed in the testis and like myosin VI, accumulates on these cones. We have investigated the possibility that Acam is a testis-specific light chain of Drosophila myosin VI. We find that Acam and myosin VI precisely colocalize at the leading edge of the actin cones and that myosin VI is necessary for this Acam localization. Further, myosin VI and Acam co-immunoprecipitate from the testis and interact in yeast two-hybrid assays. Finally Acam binds with high affinity to peptide versions of both myosin VI light chain binding sites. In contrast, although Drosophila CaM also shows high affinity interactions with these peptides, we cannot detect a CaM/myosin VI interaction in the testis. We conclude that Acam and not CaM acts as a myosin VI light chain in the Drosophila testis and hypothesize that it may alter the regulation of myosin VI in this tissue.

Received for publication, March 6, 2006 , and in revised form, May 23, 2006.

We dedicate this article to the memory of Paige Pavlik, who died February 19, 2005.

^* This work was supported by National Institutes of Health Grant GM 60494 (to K. G. M.), National Institutes of Health Grant HD39766 (to K. M. B.), and Grant C-1119 from the Welch Foundation of Texas (to K. M. B.). 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.

¹ Both authors contributed equally to the studies presented here.

² Supported by a National Research Service Award.

³ To whom correspondence should be addressed: Dept. of Biochemistry and Cell Biology, Rice University, MS-140, PO Box 1892, Houston TX 77251. Tel.: 713-348-4016; Fax: 713-348-5154; E-mail: kate{at}bioc.rice.edu.

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