Penn, C.W.

pylori urease promoter transcription nickel protein strain sequence helicobacter expression colony res gene helicobacter pylori region transcriptional c tract variation activity phase binding regulation tract wild-type fragment urea promoter nickel-responsive system urease expression phase variation position clone medium induction mod gene microbiol pylori nikr urease activity study enzyme concentration rt-pcr wild-type h nickel-responsive induction presence growth wild-type strain table control urease enzyme activity level locus immun uptake transcriptional phase variation result 5 end fusion restriction translational vliet pathogen helicobacter pylori bacteriol strep-nikr primers mod genes primer absence transcriptional level 50/ urea promoters nixa promoter bacteria strep-nikr protein repressor pylori strain 1061 operator nikr protein lacz expression res orf dnase