TOPOISOMERASE-I OF HELICOBACTER-PYLORI - JUXTAPOSITION WITH A FLAGELLIN GENE (FLAB) AND FUNCTIONAL REQUIREMENT OF A 4TH ZINC-FINGER MOTIF

Cloning and nucleotide sequence analysis showed that in Helicobacter p ylori the gene encoding topoisomerase I (topA) lies about 170 nucleoti des upstream from flaB, a gene encoding one of the two flagellin prote ins that is required for virulence. The topA and flaB genes are diverg ently transcribed. The orientation and spatial relationship between fl aB and topA are remarkably conserved among strains of a bacterium in w hich genomic rearrangements are common. The deduced amino acid sequenc e of topoisomerase I revealed four zinc finger motifs, one more than h as been reported previously for the Escherichia coil homologue. The ad ditional motif, which is near the C-terminus of the protein, appears t o be essential for function since mutations in that region are lethal. These data show that TopA proteins can be divided into several classe s on the basis of zinc finger motifs and raise the interesting possibi lity that the H. pylori enzyme has local topological effects focussed on a flagellin gene. (C) 1998 Elsevier Science B.V.