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SUBCELLULAR LOCALIZATION OF RICKETTSIAL INVASION PROTEIN, INVA

To understand further the molecular basis of rickettsial host cell invasion, Rickettsia prowazekii invasion gene homolog (invA) has been characterized. Our previous experiments have shown that InvA is an Ap₅A pyrophosphatase, a member of the Nudix hydrolase family, which is up-regulated during the internalization, early growth phase, and exit steps during rickettsial mammalian cell infection. In addition to the molecular characterization, subcellular localization of InvA was investigated. InvA-specific antibodies were raised in mice and used for immunoelectron microscopy. The generated antibodies were shown to recognize InvA and by immunogold labeling showed InvA in the cytoplasm of rickettsiae. A cytoplasmic location for InvA would allow for a rapid response to any internal substance and efficient functioning in hydrolysis of toxic metabolic by-products that are accumulated in the rickettsial cytoplasm during host cell invasion. Protecting bacteria from a hazardous environment could enhance their viability and allow them to remain metabolically active, which is a necessary step for the rickettsial obligate intracellular lifestyle.

Received May 20, 2002. Accepted for publication August 8, 2002.

Financial support: This study was supported in part by National Institutes of Health grant AI 17828. Jariyanart Gaywee received pre-doctoral support from the Royal Thai Army, Ministry of Defense, Thailand.

Reprint requests: Abdu F. Azad, Department of Microbiology and Immunology, School of Medicine, University of Maryland, 655 West Baltimore Street, Baltimore, MD 21201, Telephone: 410-706-3335, Fax: 410-706-0282, E-mail: aazad{at}umaryland.edu

Authors’ addresses: Jariyanart Gaywee, Department of Microbiology, Armed Forces Research Institute of Medical Sciences, Bangkok 10400, Thailand. John B. Sacci, Jr, Suzana Radulovic, Magda S. Beier, and Abdu F. Azad, Department of Microbiology and Immunology, School of Medicine, University of Maryland, 655 West Baltimore Street, Baltimore, MD 21201.

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