Nitrogen is often a limiting growth factor for microorganisms, thus growing in nitrogen limiting conditions is a challenge. To scavenge for nitrogen fungi will begin to grow hyphae or psuedohyphae which are also part of the induction of pathogenicity. The signal for this change in growth has been observed to come from the Mep2 ammonium transport membrane protein, a member of the Ammonium transport proteins (Amt), Methylamine permeases (Mep) and Rhesus proteins (Rh) superfamily found in all kingdoms of life. The overall structure of these proteins is highly conserved including specific amino acids lining their hydrophobic pore. Using in vivo yeast complementation, in vitro electrophysiology and in silico molecular dynamics simulations it has been found that the twin his motif, found in the centre of the pore, plays an important role in the mechanism and selectivity of Mep2. Mutations to the twin his motif switches Mep2 from a highly selective ammonium transporter to an unselective ion channel. This change has also been shown to abolish the induction of filamentous growth. This leads to the conclusion filamentous growth is not triggered by a signal cascade following ammonium translocation but rather by the specific mechanism of transport.