ABSTRACT
Because manganese performs so many vital cellular functions, all organisms have evolved with specialized systems devoted to the uptake and acquisition of this trace metal. Accumulation of manganese must also fall under tight control, since the metal is potentially toxic. There-
fore, in many instances the uptake of manganese is regulated by the bioavailability of the metal. In this chapter, examples will be provided for both bacterial and fungal manganese transporters that are acti vated or repressed in response to metal ion availability. In certain cases, the molecular basis of this regulation is understood, and both tran scriptional and posttranslational levels of control are evident.
