Whilst the autophosphorylated, activated state of GCN2 is thought to be common to all routes, it is not certain what pathways take precedence, whether they are mutually exclusive, whether they are present in all eukaryotic organisms, or whether they may be facilitated in vivo by GCN20 and GCN1. In non-starvation conditions, it is assumed that the P-stalk associates both the ribosome and translation factors around the A-site, whilst GCN1, GCN2, and GCN20 remain unbound to the ribosome in the cytosol. GCN2 remains autoinhibited, whilst GCN1 and GCN20 form a stable heterodimer. From this state, there are at least three possible routes to activation of GCN2 upon depletion of amino acids. Firstly in the case of stalled ribosomes; it may be that there is an increased affinity for the GCN1/2/20 complex for the stalled ribosome, causing an association and activation of GCN2. An alternate route to a stalled ribosome may be UV radiation. Secondly, upon starvation the P-stalk C-terminal tails may be free to bind to GCN2 due to the loss of translation factors — or alternative stresses (such as UV radiation) may also cause P1/P2 proteins to associate with uL10, forming the P-stalk and activating GCN2 in this manner. Thirdly, the increase in deacylated tRNA levels may cause an associated with GCN2, causing it to become activated in a manner that involves GCN1 and GCN20. Additionally, all three of these routes may combine, or be only partially correct.