Abstract
Age-related changes in proteins expressed in the cytosol of rat brain were investigated. When brains from 14-day-old embryos and 2-year-old rats were compared, we found more than 30 embryo-specific proteins expressed in embryonic rat brain. Of these proteins, we studied a protein, estimated with sodium dodecylsulfate-polyacrylamide gel electrophoresis to have a molecular weight of 40 kDa, which decreased with embryonic development and then disappeared within 2 weeks after birth. Partial amino acid sequences of the rat 40-kDa protein were identical to those of 40 kDa, the putative human leukocyte antigen (HLA) -DR-associated protein (PHAP) II. To amplify and clone the cDNA of the 40-kDa protein, reverse transcription polymerase chain reaction was carried out. At least three partial cDNA clones were obtained. The amino acid sequences deduced from these clones showed a high degree of homology with PHAPII, but a small nucleotide deletion was observed in two of them. These results indicate that the fetal rat-specific 40-kDa protein might be a rat homologue of human PHAPII and suggest that at least three minor isotypes are present in the brain. Although the function of PHAPII is unclear, the PHAPII homologue might play an important role in the development of the central nervous system in the rat.
