TABLE 3.

Factors effecting phosphorylation of the components of the HrrSA and ChrSA systems

TCS protein	Phosphorylation activity
	In vitro					In vivod
	ChrSa	HrrSa	Auto-Pb	Auto-de-Pb	DNA bindingc
ChrA	Yes	No	No	Yes	Yes	Not detected
HrrA	Yes	No	No	No	No	Yes
ChrS			Yes	No		Not determined
HrrS			No	Not determined		Not detected

^aChrS and HrrS were assessed for their ability to transphosphorylate ChrA and HrrA.

^bProteins were examined for ability to autophosphorylate (auto-P) and autodephosphorylate (auto-de-P) in vitro.

^cRequirement for phosphorylation of the RR to bind DNA (determined by EMSA). ChrA and HrrA bind to identical sequences upstream of the hmuO and hemA genes.

^dIn vivo phosphorylation of ChrA was not detected, which is likely due to rapid dephosphorylation. In vivo phosphorylation of HrrA was associated with both ChrS and HrrS and occurred in the presence and absence of Hb. Phosphorylation for ChrS was not determined, due to the inability to observe ChrS in vivo because of the limitations of the Western blot system. Phosphorylation of HrrS in vivo was not detected.