It is thought that around 30% of known PPs are present in all tissues, with the rest showing some level of tissue restriction. While protein phosphorylation is a cell-wide regulatory mechanism, recent quantitative proteomics studies have shown that phosphorylation preferentially targets nuclear proteins. Many PPs that regulate nuclear events, are often enriched or exclusively present in the nucleus. In neuronal cells, PPs are present in multiple cellular compartments and play a critical role at both pre- and post-synapses, in the cytoplasm and in the nucleus where they regulate gene expression.
iT Is thouGhT tHat around 30% oF knOWn pPs ARe pResenT in ALl TIssues, wIth the rest showInG soMe level of tiSsue rEstrICTion. whIle pRotEin PhoSphORylatIon is a cELl-widE regulatoRY mEChaNism, rEcEnt QUantitATIVE pRoTEomIcs studieS haVe shown that phospHorylatiON prEFerentiAlly targeTs nUClear ProTeIns. mAny pps that ReGUlate nuclear eVents, aRe ofteN enRiCHED OR excluSivEly presEnT In tHe nucleus. in nEurOnal cells, pps arE pRESeNt in muLTiPle cElluLaR coMpaRtMentS and PLAY a CriTIcaL Role at both pRe- and Post-sYnapses, iN ThE cytoplasm aNd In the NucleuS wHere thEy rEGulate genE expRessiOn.