Ref ID : 7414
Ji Young Choi, Tae Won Lee, Kwang W. Jeon, and Tae In Ahn; Evidence for Simbiont-induced Alteration of a Host's Gene Expression: Irreversible Loss of SAM Synthetase from Amoeba proteus. J.Eukaryot.Microbiol. 44(5):412-419, 1997
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Symbiont-bearing xD amoebae no longer produce a 45-kDa cytoplasmic protein that function as S-adenosylmethionine synthetase in symbiont-free D amoebae. The absence of the protein in xD amoebae is attributable to xD amoeba's failure to transcribe the corresponding gene as a result of harboring bacterial symbionts. However, xD amobae have about half the level of enzyme activity found in D amoebae, indicating that they use an alternative source for the enzyme. xD amoebae originated from D amoebae by bacterial infection and now depend on their symbionts for survival. xD amoebae exhibit irreversible nucleolar abnormalities when their symbionts are removed, suggesting that X-bacteria supply the needed enzyme. A monoclonal antibody against the 45-kDa protein was produced and used as a probe in cloning its corresponding cDNA. The product of the cDNA was found to have S-adenosylmethionine synthetase activity. These results show how symbiotic X-bacteria may become essential cellular components of amoebae by supplementing a genetic defect for an amoeba's house-keeping gene that is brought about by an action of X-bacterial themselves. This is the first reported example in which symbionts alter the host's gene expression to block the production of an essential protein.