Abstract
To isolate proteins / genes which might be involved in the development of the central nervous system, we analyzed proteins expressed transiently in the fetal rat brain, we previously reported that several proteins including putative“human-leukocyte associated ( HLA) ”Class II associated proteins (PHAP I and PHAP II ) which have been purified from the cytosolic fraction of the human lymphoblastoid B-cell line H2LCL and bind to the intracellular domain of the HLA class II were expressed predominantly in the fetal rat brain and decreased in the adult rat. In this study we attempted to identify target proteins in the fetal rat brain cytosolic fraction which might interact with PHAP I and PHAP II to understand the physiological roles of PHAP I and PHAP II . We detected several PHAP I and PHAP II binding proteins from the cytosolic fraction of the fetal rat brain with an affinity gel using recombinant PHAP I and PHAP II as a ligand. We also found protein serine kinase activity in these binding proteins which phosphorylates PHAP I protein. Recently, it has been reported that PHAP I and PHAP II have multiple functions in cells such as human pp 32, APRIL (acidic protein rich in leucines), bovined I1PP2A, rat LANP (leucine-rich acidic nuclear protein), and SET, I2PP2A, template activating factor I (TAF-1) . In this study, we suggest that PHAP I serine kinase regulates PHAP I activity.
