Evidence for symbiont-induced alteration of a host's gene expression: irreversible loss of SAM synthetase from Amoeba proteus.
Symbiont-bearing xD amoebae no longer produce a 45-kDa cytoplasmic protein that functions 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 amoebae 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 amoeba by supplementing a genetic defect for an amoeba's house-keeping gene that is brought about by an action of X-bacteria themselves. This is the first reported example in which symbionts alter the host's gene expression to block the production of an essential protein.
Choi
J Y
JY
Department of Biology Education, Seoul National University, Korea.
Lee
T W
TW
Jeon
K W
KW
Ahn
T I
TI
D000595:Amino Acid Sequence; D000656:Amoeba / Q000201:enzymology* / Q000235:genetics / Q000382:microbiology; D000818:Animals; D000911:Antibodies, Monoclonal; D000913:Antibodies, Protozoan; D001419:Bacteria / Q000201:enzymology; D018407:Bacterial Physiological Phenomena; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000032:analysis; D016054:DNA, Protozoan / Q000032:analysis; D015971:Gene Expression Regulation, Enzymologic; D008716:Methionine Adenosyltransferase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D008970:Molecular Weight; D012333:RNA, Messenger / Q000032:analysis; D016053:RNA, Protozoan / Q000032:analysis; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013559:Symbiosis
D000911:Antibodies, Monoclonal; D000913:Antibodies, Protozoan; D018076:DNA, Complementary; D016054:DNA, Protozoan; D012333:RNA, Messenger; D016053:RNA, Protozoan; D008716:Methionine Adenosyltransferase