Detection of the Wolbachia-encoded DNA binding protein, HU beta, in mosquito gonads

Wolbachia are obligate intracellular bacteria that cause cytoplasmic incompatibility in mosquitoes. In an incompatible cross, eggs of uninfected females fail to hatch when fertilized by sperm from infected males. We used polyacrylamide gel electrophoresis and tandem mass spectrometry to identify Wolbachia proteins in infected mosquito gonads. These included surface proteins with masses of 25 and 18 kDa and the DNA binding protein, HU beta. Using reverse transcriptase polymerase chain reaction, we showed that the HU gene is transcribed in Wolbachia-infected Culex pipiens and Aedes albopictus mosquitoes. We sequenced HU genes from four Wolbachia strains and compared deduced protein sequences with additional homologs from the databases. Among the Rickettsiales, Wolbachia HU has distinct N- and C-terminal basic/acidic amino acid motifs as well as a pair of conserved, cysteine residues.

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► Wolbachia express a DNA binding protein, HU, in mosquito testes and ovaries.
► HU abundance is comparable to that of Wolbachia surface proteins.
► Wolbachia HU has unique amino acid motifs absent in Escherichia coli homologs.
► HU is the first Wolbachia DNA binding protein detected by mass spectrometry.