Pur alpha protein implicated in dendritic RNA transport interacts with ribosomes in neuronal cytoplasm.

We have previously reported that pur alpha, known to be a regulator of DNA replication and transcription, links neural BC1 RNA to microtubules via dendrite-targeting RNA motifs. Here we demonstrate the subcellular localization of pur proteins within the brain. Pur proteins were detected in neurons but not in glia. Immunohistochemical staining was prominent in perikarya and proximal dendrites and also extended into primary dendritic processes, but no significant signals were detected in the distal regions of dendrite. When homogenates of mouse brain were fractionated, pur alpha was most concentrated in the microsomal pellet. Consistently, pur alpha co-fractionated with free polysomes as well as with membrane-bound polysomes and the association with polysomes was mediated by binding ribosomal subunits. Levels of ribosomes with pur alpha progressively increased during postnatal development of the brain.