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First published online 6 January 2004
doi: 10.1242/jcs.00894

Journal of Cell Science 117, 535-543 (2004)
Published by The Company of Biologists 2004
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Research Article

Gene switching in Amoeba proteus caused by endosymbiotic bacteria

Taeck J. Jeon and Kwang W. Jeon*

Department of Biochemistry, University of Tennessee, Knoxville, Tennessee 37996, USA

* Author for correspondence (e-mail: jeon{at}utk.edu)

Accepted 19 September 2003

The expression of genes for S-adenosylmethionine synthetase (SAMS), which catalyzes the synthesis of S-adenosylmethionine (AdoMet), a major methyl donor in cells, was studied in symbiont-free (D) and symbiont-bearing (xD) amoeba strains to determine the effect of bacterial endosymbionts. The symbionts suppressed the expression of the gene in host xD amoebae, but amoebae still exhibited about half the enzyme activity found in symbiont-free D amoebae. The study was aimed at elucidating mechanisms of the suppression of the amoeba's gene and determining the alternative source for the gene product. Unexpectedly, we found a second sams (sams2) gene in amoebae, which encoded 390 amino acids. Results of experiments measuring SAMS activities and amounts of AdoMet in D and xD amoebae showed that the half SAMS activity found in xD amoebae came from the amoeba's SAMS2 and not from their endosymbionts. The expression of amoeba sams genes was switched from sams1 to sams2 as a result of infection with X-bacteria, raising the possibility that the switch in the expression of sams genes by bacteria plays a role in the development of symbiosis and the host-pathogen interactions. This is the first report showing such a switch in the expression of host sams genes by infecting bacteria.

Key words: Amoeba, Symbiosis, S-adenosylmethionine (AdoMet), S-adenosylmethionine synthetase (SAMS), Gene switching, Endosymbionts




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