A NEW CLASS OF RNP PARTICLES CONTAINING SMALL RNA HOMOLOGOUS TO SHORTINTERSPERSED DNA REPEATS

Rat tissues and stable cell lines such as human A431 and K562 were sho wn to harbor small RNP particles (alpha RNP) with common physicochemic al features but distinct in composition and properties from other RNPs known. The alpha RNP contained small RNA transcribed by RNA polymeras e III and homologous to short interspersed repetitive DNA sequences (r odent ID, B1, B2, and human Alu), together with a characteristic set o f proteins (20-48K) including common (La antigen) and specific compone nts. The alpha RNA could hybridize with rat tyrosine aminotransferase gene fragments and with specific mRNAs; their content in the cell was regulated by glucocorticoid hormones as well in the course of cell dif ferentiation. It is suggested that alpha RNA belongs to a new class of regulatory RNA and that alpha RNP are involved in coordinated control of the expression of gene sets with SINE-homologous sequences in thei r regulatory regions.