Intracellular localization and in vivo trafficking of p24A and p23

Recently, p24A and p23 (also termed Tmp21), two members of the p24 protein family, have been proposed to function as integral receptors for the COPI-v esicle coat. This study describes the intracellular localization and traffi cking of p24A in comparison to p23, For immunolocalization of p24A and p23, strong reduction and denaturation conditions were necessary to allow antib ody interaction. Both p24A and p23 cycle continuously between intermediate compartment (IC) elements and the cis-Golgi network. In vivo trafficking of p24A and p23 tagged to green fluorescent protein (GFP) revealed that both proteins travel by large (up to 1 mu m in length) microtubule-dependent pre -Golgi carriers with a maximum speed of up to 1.6 mu m s(-1) from the IC to the Golgi cisternae, Aluminum fluoride, a general activator of heterotrime ric G-proteins, blocked peripheral pre-Golgi movements of GFP-p24A/p23 and inhibited fluorescence recovery after photobleaching in the perinuclear Gol gi area. p24A and p23 are predominantly colocalized, Overexpression of GFP- p24A, to an extent which did not destroy the Golgi complex, induced delocal ization of part of the proteins into ER elements, This study therefore give s new insights into the localization and trafficking behavior of the two CO PI-binding proteins p24A and p23.