Brain-specific small RNA transcript of the identifier sequences is present as a 10 S ribonucleoprotein particle.

BC-1 RNA is a small RNA transcript of the identifier repetitive sequences present in rodent genomes. The RNA has been reported to be specific to the brain and confined to the cytoplasm. The RNA level increases during the 1st month after birth. To understand its cytoplasmic function, it seems important to examine whether BC-1 RNA is present as an RNP. It is believed that the protein component may govern the functions of BC-1 RNA in the brain cells. In the present report, we have demonstrated that BC-1 RNA is not free but complexed with proteins to form a 10 S RNP in the cytoplasm. We have also shown that the 10 S RNP is not associated with cytoplasmic structures such as polysomes/ribosomes or microsomes. The buoyant density of the RNP was 1.26 g/cm3 in metrizamide. Furthermore, some of the protein components were shown to be in direct contact with RNA, since photo-cross-linking adducts of protein to BC-1 RNA were identified upon UV irradiation of the 10 S BC-1 RNP.