The DRB1 proteins from all 3 species contain 476 amino acids and have predicted molecular masses of 53 kD. Each contains 4 RRM-type RNA-binding domains, although the authors speculated that the second RNA-binding domain may be a pseudodomain based on sequence divergence. Human DRB1 shares about 92% amino acid identity with the rat protein.Expression of Drb1 in rat brain was dynamically regulated during development, with highest levels at embryonic day 16 and gradually decreasing levels into adulthood, when Drb1 expression was restricted to the cerebellum, olfactory bulb, and hippocampus. In situ hybridization of rat brain showed strong Drb1 expression at embryonic day 16 in the subventricular zone and neural tube, while at postnatal day 3, expression was seen in hippocampal pyramidal neurons and cortical neurons.