Analysis of iceA1 transcription in Helicobacter pylori

Transcription of the Helicobacter pylori iceA1 gene is induced following adherence of the bacterium to gastric epithelial cells in vitro, suggesting that this gene might be involved in H. pylori pathogenesis. Consequently, the current studies were undertaken to characterize iceA1 transcription and to define the structure of iceA1-containing transcripts to evaluate the potential of this gene to encode functional proteins.

Northern blots and primer extension of RNA isolated from broth-grown cultures of various H. pylori strains was done to analyze iceA1-specific gene transcription. Reverse transcriptase (RT)-PCR was used to determine the levels of iceA1 transcripts derived from readthrough transcription that was initiated upstream of iceA1 within the 5'-flanking cysE gene.

Three major transcripts were detected and each was initiated from a common promoter, designated PI. Two of these transcripts were comprised of iceA1 sequence, while a third transcript was dicistronic and included the downstream gene, hpyIM. In addition, 10-fold lower levels of iceA1 transcripts were initiated upstream of PI, either within or immediately downstream of cysE.

The present analysis suggests that iceA1 does not encode a functional protein in the majority of H. pylori strains. However, transcription of hpyIM, which encodes a highly conserved DNA adenine methyltransferase, is linked to iceA1 transcription. Therefore, iceA1 may affect H. pylori virulence in vivo through transcriptional regulation of hpyIM expression levels, which may result in specific variations in DNA methylation patterns leading to alteration in the expression of genes involved in virulence or pathogenesis.