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In a previous paper in this journal [Djondjurov, L., Ivanova, E. and Tsanev, R. (1979) Eur. J. Biochem. 97, 133–139], we showed that a nuclear fraction released from chromatin under a mild nuclease digestion contained an increased amount of hnRNA and the bulk of nonhistone proteins with a high metabolic rate. The present investigation has revealed that the nonhistone proteins of this fraction could be divided into three distinct metabolic groups. The first group consists of proteins with a fast turnover rate (mean half-life 30 min) which migrate into chromatin immediately after their synthesis. These proteins are predominantly acid-soluble and have relatively high molecular weights. The second group includes proteins which migrate to the nucleus more slowly and metabolize with a moderate turnover rate (mean half-life 5 h). The third group contains proteins with a more conservative metabolic behaviour. In experiments with actinomycin D it was found that the bulk of the nonhistone proteins of this fraction are not real components of the chromatin but belong to the protein moiety of heterogeneous nuclear ribonucleoprotein particles associated with chromatin. [ABSTRACT FROM AUTHOR]

It is well know that protein synthesis stopped either by chloromycetin or by starvation of an essential amino acid for a RC relstrain, ribosomal RNA synthesis continues, but products do not appear in 50 S and 30 ribosomes. It has also been shown that 5 S RNA synthesis is altered by the addition of chloromycetin but in an unknown manner. In this paper we report that: (a) during amino-acid starvation of a starvation of RCrel strain of Escherichia coli, 5 S RNA is transcribed as 5 S relax RNA located outside the ribosomes, in the supernatant fraction; (b) this 5 S RNA which is slightly longer than the normal product is convertible into a true 5 S RNA when protein synthesis is restored after blockage of RNA synthesis by actinomycin ;(c) part of the 23 S RNA from a 25 S particle appears after resumption of protein synthesis in a 40 S parcel which contains normal 5S RNA; (d) a pool of 5 S precursor RNA exists outside the 50 S ribosome. This 5 S precursor RNA is isolated; (e) this precursor which is isolated from the 105000xg supernatant fraction after pulse labeling, migrates on gel electrophoresis between 5 S relax RNA and true 5 S RNA. [ABSTRACT FROM AUTHOR]

The effect of actinomycin D and DL-p-fluorophenylalanine on ribosome formation has been studied in exponentially growing Tetrahymena. cells. Both compounds cause inhibition of ribosome formation. However, ribosome formation is qualitatively very similar in inhibited and uninhibited cells. p-Fluorophenylalanine is incorporated into ribosomal proteins of completed ribosomal particles when used in inhibitor concentration (1 mg/ml). This demonstrates that limited modifications of ribosomal proteins, due to the presence of the amino acid analogue in the ribosomal polypeptide chains still allow the modified proteins to assemble with ribosomal RNA to give intact ribosomal particles. The p-fluorophenylalanine containing ribosomes have normal physical-chemical properties with respect to dissociation into sub-units by dialysis against low Mg++ concentration, sedimentation values in sucrose gradients and buoyant density in isopycnic CsCl gradients. The regulatory aspects of ribosome biosynthesis in the light of the present results are discussed. [ABSTRACT FROM AUTHOR]