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Cell Biology International (1999) 23, 719728 (Printed in Great Britain)
THE TETRAHYMENA HOMOLOG OF BACTERIAL AND MAMMALIAN 4-HYDROXYPHENYLPYRUVATE DIOXYGENASES LOCALIZES TO MEMBRANES OF THE ENDOPLASMIC RETICULUM
Søren Nevea, Ditte Tornehaveb,f2, Thomas Juhl Corydonc and Karsten Kristiansena,f1
aDepartment of Molecular Biology, University of Odense, Campusvej 55, DK-5230, Odense M, Denmark
bDepartment of Anatomy and Cell Biology, Institute of Medical Biology, University of Odense, Winsløwsparken 19, DK-5000, Odense C, Denmark
cInstitute of Human Genetics, The Bartholin Building, Aarhus University, DK-8000, Aarhus C, Denmark
The expression and intracellular localization of the Tetrahymena homolog of 4-hydroxyphenylpyruvate dioxygenase (HPPD) were investigated in wild-type Tetrahymena thermophila strain B1868 VII and the mutant strains IIG8, defective in food vacuole formation, MS-1, blocked in secretion of lysosomal enzymes, and SB 281, defective in mucocyst maturation. Immunoelectron microscopy and confocal laser scanning microscopy demonstrated that Tetrahymena HPPD primarily localized to membranes of the endoplasmic reticulum. In addition, Tetrahymena HPPD was detected in association with membranes of the Golgi apparatus, and transport vesicles in exponentially growing wild-type and mutant strains. In starved cells, Tetrahymena HPPD localized exclusively to membranes of small vesicles. Since no de novo synthesis ofTetrahymena HPPD takes place in cells starved for more than 30
Key words: confocal laser scanning microscopy, F-antigen, Golgi apparatus, immunoelectron microscopy, Tetrahymena mutants, transport vesicles.
f2Present address: Department of Molecular Cell Biology, Statens Serum Institute, Artillerivej 5, Building 81, DK-2300 Copenhagen S, Denmark.
f1To whom correspondence should be addressed. Dr Karsten Kristiansen, Department of Molecular Biology, University of Odense, Campusvej 55, DK-5320 Odense M, Denmark. Tel: (+45) 6550 2408; E-mail:firstname.lastname@example.org; Fax: (+45) 65 93 27 81.
Received 23 September 1998; accepted 4 December 1998doi:10.1006/cbir.1998.0336