Low‐abundance 32‐kilodalton nuclear protein specifically enriched in the central nervous system

Recently, a low‐abundance nuclear protein, p32/6.3, has been identified in brain tissue (Egle and Shelton: Journal of Biological Chemistry 261:2294–2298,1986). Using a Western blot procedure, we describe its distribution in the nervous system, determine its relative enrichment in brain versus liver, kidney, and certain other tissues, and describe an isolation procedure from brain. Selective enrichment occurs in basal ganglia, diencephalon, hippocampus, cerebellum, brainstem, spinal cord, and cerebral cortex but not in retina, dorsal root ganglia, and sympathetic ganglia. Thus, enrichment is limited to areas of the central nervous system. p32/6.3 appears to be preferentially enriched in neurons, because in bulk‐isolated fractions from rat grey matter it is more abundant in neuron‐enriched fractions than in astrocyte‐enriched fractions. p32/6.3 is approximately 20‐fold more concentrated in an insoluble nuclear protein or matrix fraction from forebrain than from kidney, liver, adrenal gland, or retina. This degree of enrichment is an ancient trait, detectable in the chicken as well as mammals.