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Translation of cellular and early vaccinia RNA in nuclease-treated lysates, derived from uninfected and vaccinia-virus-infected cells al the early stage, has been investigated. When using limiting amounts of RNA no discrimination of translation was observed in the infected cells lysates; This conclusion was confirmed by sensitive RNA competition experiments for translation in vitro and also when using two different fractionated systems for protein synthesis in vitro. This absence of detectable discrimination in vitro was established both by comparing incorporation of [35S]methionine into proteins and by analysis of the products thus synthesized by sodium dodecylsulfate gel electrophoresis. However, a modification of the translational machinery from vaccinia-virus-infected cells did occur since only the ribosomal salt wash derived from infected cells was able to reverse the inhibition of protein synthesis in vitro resulting from excess RNA (control or early). This property of vaccinia-virus-infected cell lysates may result from the synthesis of an early protein involved in translation or from a better recovery of translational factors from the infected cells., as suggested in the accompanying paper. [ABSTRACT FROM AUTHOR]

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]

When Escherichia coli 30-S ribosomal subunits are hydrolysed under mild conditions, two ribonucleoprotein fragments of unequal size are produced. Knowledge of the RNA sequences contained in these hydrolysis products was required for the experiments described in the preceding paper, and the RNA sub-fragments have therefore been examined by oligonucleotide analysis. Two well-defined small fragments of free RNA, produced concomitantly with the ribonucleoprotein fragments, were also analysed. The larger ribonucleoprotein fragment, containing predominantly proteins S4, S5, S8, S15, S16 (17) and S20, contains a complex mixture of RNA sub-fragments varying from about 100 to 800 nucleotides in length. All these fragments arose from the 5′-terminal 900 nucleotides of 16-S RNA, corresponding to the well-known 12-S fragment. No long-range interactions could be detected within this RNA region in these experiments. The RNA from the smaller ribonucleoprotein fragment (containing proteins S7, S9, S10, S14 and S19) has been described in detail previously, and consists of about 450 nucleotides near the 3′ end of the 16-S RNA, but lacking the 3′-terminal 150 nucleotides. The two small free RNA fragments (above) partly account for these missing 150 nucleotides; both fragments arose from section A of the 16-S RNA, but section J (the 3′-terminal 50 nucleotides) was not found. This result suggests that the 3′ region of 16-S RNA is not involved in stable interactions with protein. [ABSTRACT FROM AUTHOR]

The chromatin structure of the macronuclear genes encoding ribosomal proteins S25 and L1 in the ciliated protozoan Tetrahymena thermophila was analyzed. Using the indirect end-labelling technique, DNase-I-hypersensitive regions were located in the promoter regions as well as in the 3' regions of the genes. The DNase-I-hypersensitive regions were present in chromatin of exponentially growing cells, where the rate of ribosomal-protein gene transcription is high, and in chromatin from starved cells, where transcription of ribosomal-protein genes is severely depressed. Micrococcalnuclease-digestion experiments revealed that the promoter regions of the S25 gene and the L1 gene are devoid of nucleosomes in exponentially growing cells. In starved cells, no nucleosomal organisation of the promoter region of the L1 gene could be detected, whereas nucleosomal structures were discernible in the promoter region of the S25 gene. A conspicuous polypurine sequence motif, AARGGGAAA, is present within or adjacent to the DNase-I-hypersensitive regions in the promoter of the S25 and the L1 gene, and interestingly, the same motif is found also in the promoter regions of the genes encoding ribosomal proteins L21 and L37. [ABSTRACT FROM AUTHOR]

Reports on the cleavage of rRNA by the treatment of ribosomes in reticulocyte lysates with low concentrations of the calcium-dependent nuclease from Staphylococcus aureus. Localization of the positions of the cleaved phosphodiester bonds by primer extension and polyacrylamide gel electrophoresis; Reason for the decrease in translational activity observed in lysates treated with low amounts of S. aureus nuclease; Suggestion that the induced cleavages were not detrimental to ribosomal function but could influence the rate of ribosomal movement along the messenger RNA.

We have been able to isolate several species of 5-S ribosomal RNA from Eschzerichia coli A19. These molecules were separated on the basis of their differing stabilities during electrophoresis on 12% polyacrylamide gels in 7 M urea. This differing stability is shown, in one case, to be due to a different primary sequence. We have determined the sequence of the least stable of these molecules and have found only one difference to the published sequence of E. coli A19 5-S RNA, namely a uridine in place of a cytidine at position 92. The consequent G U base pair, formed in a normally highly stable G. C-rich region. is responsible for a drastic reduction in the stability of the molecule. This instability leads to a less constrained, more compact molecule which thus migrates laster in electrophoresis under denaturing conditions. This species of 5-S RNA is shown to make up 30% of the total 5-S RNA in the 50-S ribosomal subunits in this organism. Further structural studies were carried out using S1 nuclease digestion, sodium bisulphite modification and thermal melting analysis. All these methods indicate a 5-S RNA drastically destabilized in parts of its secondary and tertiary structure. Finally, the ability of the variant 5-S RNA to recognize and form a complex with its 50-S subunit binding proteins was examined and found to be impaired. [ABSTRACT FROM AUTHOR]

The extrachromosomal DNA coding for the ribosomal RNA precursor in Tetrahymena contains a transcribed region with a size of 6 x 10[sup3] base pairs plus non-transcribed central and distal spacers. In the present study the chromatin structure of the transcribed region and the terminal spacer have been compared. Micrococcal nuclease and DNase I were used to investigate the nucleosomal and the higher order structures. The specific DNA fragments were visualized by gel electrophoresis, Southern blotting onto nitrocellulose sheets and hybridization with specific [sup32]P-labelled RNA probes. Investigations of the cleavage patterns demonstrate the presence of a defined nucleosomal structure in the non-transcribed region, while there is no indication of a nucleosomal pattern in the transcribed region. Specific regions on the r-chromatin are hypersensitive to DNase I. The first cleavage occurs in the non-transcribed central spacer region, while the second cleavage takes place in a region near the 3[sup'] end. The hypersensitivity of the central part of r-chromatin is also found by autodigestion in isolated nucleoli. [ABSTRACT FROM AUTHOR]

Netropsin binds to DNA in caesium chloride density gradients and reduces the density of the DNA. The DNA is saturated at a netropsin/DNA weight ratio of about 6 and the change in density, Δ..., at saturation is given by Δ... = - 109 (dA + dT content)1.87 mg/ml for the six DNAs tested covering dA +dT contents from 0.28 to 0.69. At lower netropsin/DNA ratios the observed density shifts are consistent with a two-site model for netropsin binding to DNA. Netropsin approximately doubles the resolution of Physarurn polycephalum nucleolar satellite DNA from main-band DNA. The fragments of P. polycephalum nucleolar satellite DNA obtained with the restriction endonuclease HindIII do not separate on CsCl gradients, even in the presence of netropsin, which shows that the transcribed and non-transcribed sequences in this DNA have similar nucleotide compositions. [ABSTRACT FROM AUTHOR]