Helicobacter pylori strains possessing cagA are associated with peptic
ulceration. To understand the regulation of expression of cagA, picB,
associated with interleukin-8 induction, and ureA, encoding the small
urease subunit, we created gene fusions of cagA, ureA, and picB of st
rain 3401, using a promoterless reporter (xylE). Expression of XylE af
ter growth in broth culture revealed that basal levels of expression o
f cagA and ureA in H. pylori were substantially greater than for picB.
For cagA expression in stationary-phase cells, brief exposure to acid
pH caused a significant increase in xylE expression compared with neu
tral pH. In contrast, expression of xylE in ureA or picB decreased aft
er parallel exposure to acid pH (pH 7 > 6 > 5 > 4), regardless of the
growth phase. Expression of the CagA protein varied with growth phase
and pH exposure in parallel with the observed transcriptional variatio
n, The concentration of CagA in a cell membrane-enriched fraction afte
r growth at pH 6 was significantly higher than after growth at pH 5 or
7. We conclude that the promoterless reporter xylE is useful for stud
ying the regulation of gene expression in H. pylori and that regulatio
n of CagA production occurs mainly at the transcriptional level.