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Abstract
The gene (sdhA) coding for the flavoprotein subunit (SdhA) of succinate dehydrogenase
of the obligate intracellular parasitic bacterium, Rickettsia prowazekii, has been
isolated using an oligodeoxyribonucleotide probe to the conserved flavin adenine dinucleotide
(FAD)-binding region of characterized flavoproteins. Nucleotide (nt) sequence analysis
revealed an open reading frame (ORF) of 1791 bp capable of encoding a protein of 596
amino acids (aa) with a deduced M(r) of 65,444. The deduced aa sequence, when compared
to the flavoprotein subunits of Escherichia coli, Bacillus subtilis, Saccharomyces
cerevisiae and Bos taurus, revealed 52.8, 34.0, 65.8 and 52.0% aa identity, respectively.
R. prowazekii SdhA produced in E. coli minicells and analyzed by sodium dodecyl sulfate-polyacrylamide-gel
electrophoresis (SDS-PAGE) migrated as a protein of approximately 63 kDa, comparable
to the size of the deduced protein. In addition, two proteins of approximately 12
and 41 kDa were also produced in the E. coli minicells. The production of these proteins
resulted from additional translational starts within the SdhA coding sequence, suggesting
differences between the translational start signals of E. coli and R. prowazekii.
Despite the similarity of R. prowazekii SdhA to that of E. coli, the R. prowazekii
SdhA did not complement an E. coli sdhA mutant. In addition, analysis of the nt sequence
immediately upstream from R. prowazekii sdhA revealed that the rickettsial sdh gene
organization differs from that of E. coli and B. subtilis.