(I) When fully dephosphorylated in the presence of a high
calcium ion concentration, CrzA is in the most active state, strongly localized
to the nucleus and able to efficiently interact with the promoters of target
genes to enable transcription following calcium stimulation. (II)
When the N-terminal regulatory domain is phosphorylated, nuclear translocation
is attenuated, but some protein may still enter the nucleus and bind efficiently
to target genes. (III) When the DBD is phosphorylated, CrzA
translocates to the nucleus, but efficiency of binding to target genes may be
reduced. The high amount of nuclear protein present may enable sufficient
expression of target genes. (IV) When CrzA is fully phosphorylated,
both nuclear translocation and DNA-binding efficiency may be impaired, leading
to insufficient activation of target gene expression and consequent phenotypic
defects.