Depletion in nuclei of proteins associated with hnRNA, as a result of inhibition of RNA synthesis

The effect of the administration of three inhibitors of RNA synthesis, α-amanitin, actinomycin D and galactosamine, on rat liver nuclear non-histone proteins has been investigated. A selective depletion of one group of proteins having a mol. wt of between 30 and 45 thousand Daltons is observed, the degree of which is dependent on the degree of inhibition of RNA synthesis. These proteins constitute a major part of the RNP complexes associated with heterogeneous nuclear RNA (hnRNA) (informoferes). Secondary impairment of protein synthesis cannot be the cause of their depletion, as cycloheximide does not significantly affect them. We conclude that specific informofere proteins are stored in the cytoplasm and enter the nucleus during activation of transcription to associate with the hnRNA.