ABSTRACTCarbon storage regulator A ofBorrelia burgdorferi(CsrABb) contributes to vertebrate host-specific adaptation by modulating activation of the Rrp2-RpoN-RpoS pathway and is critical for infectivity. We hypothesized that the functions of CsrABbare dependent on environmental signals and on select residues. We analyzed the phenotype ofcsrABbdeletion and site-specific mutants to determine the conserved and pathogen-specific attributes of CsrABb. Levels of phosphate acetyltransferase (Pta) involved in conversion of acetyl phosphate to acetyl-coenzyme A (acetyl-CoA) and posttranscriptionally regulated by CsrABbin thecsrABbmutant were reduced from or similar to those in the control strains under unfed- or fed-tick conditions, respectively. Increased levels of supplemental acetate restored vertebrate host-responsive determinants in thecsrABbmutant to parental levels, indicating that both the levels of CsrABband the acetyl phosphate and acetyl-CoA balance contribute to the activation of the Rrp2-RpoN-RpoS pathway. Site-specific replacement of 8 key residues of CsrABb(8S) with alanines resulted in increased levels of CsrABband reduced levels of Pta and acetyl-CoA, while levels of RpoS, BosR, and other members ofrpoSregulon were elevated. Truncation of 7 amino acids at the C terminus of CsrABb(7D) resulted in reducedcsrABbtranscripts and posttranscriptionally reduced levels of FliW located upstream of CsrABb. Electrophoretic mobility shift assays revealed increased binding of 8S mutant protein to the CsrA binding box upstream ofptacompared to the parental and 7D truncated protein. Two CsrABbbinding sites were also identified upstream offliWwithin theflgKcoding sequence. These observations reveal conserved and unique functions of CsrABbthat regulate adaptive gene expression inB. burgdorferi.
Involvement of His HC3 (146) beta in the Bohr effect of human hemoglobin. Studies of native and N-ethylmaleimide-treated hemoglobin A and hemoglobin Cowtown (beta 146 His replaced by Leu).