Stimulation of DNA-dependent RNA synthesis by a protein associated with ribosomes

Escherichia coli mutant strain with altered expression of the tryptophan operon: ribonucleic acid synthesis in vitro

Ribonucleic acid (RNA) synthesis has been studied in vitro with a partially purified preparation of RNA polymerase from a mutant strain of Escherichia coli with a reduced rate of accumulation of tryptophan RNA (P.H. Pouwels and H.J. Scholten, J. Bacteriol. 139:393-397, 1979). The incorporation of radioactive label into RNA with polymerase from mutant bacteria is considerably lower than that with the enzyme from wild-type bacteria. These results are explained by the presence in mutant bacteria, but not in wild-type bacteria, of a factor which suppresses the accumulation of RNA. Mutant bacteria contain a factor which renders RNA synthesis with mutant and wild-type RNA polymerase resistant to various inhibitors of RNA synthesis, e.g. rifampin, streptolydigin, and heparin. We conclude that in mutant bacteria a factor is modified which suppresses the accumulation of some RNA species and lowers the sensitivity of RNA polymerase to some transcription inhibitors.

DNA-directed synthesis in vitro of beta-galactosidase: requirement for a ribosome release factor

The DNA-directed synthesis of beta-galactosidase in Escherichia coli extracts has been investigated in a partially fractionated system. A dependency was obtained for 3',5'-cyclic AMP receptor protein and also for a factor, from the salt wash of ribosomes, that has been purified to near homogeneity. This factor has been identified with a ribosome release factor previously purified from the supernatant fraction by A. Hirashima and A. Kaji [(1972) Biochemistry 11,4037-4044]. In the coupled transcription-translation system this factor stimulates beta-galactosidase synthesis and total protein synthesis 2- to 4-fold. It is thus clear that the ribosome release factor has a physiological function in translation. It may also affect transcription, because it stimulated total RNA synthesis up to 50% in this in vitro system.

The firA gene, a locus involved in the expression of rifampicin resistance in Escherichia coli. I. Characterisation of lambdafirA transducing phages constructed in vitro

The firA200 mutation of E. coli not only renders RNA synthesis thermosensitive but also eliminates the high-level resistance to rifampicin associated with certain mutations in the beta subunit of the RNA polymerase. A priori, the firA gene is likely to code for an essential component of the transcription apparatus. The isolation is reported of transducing phages for the firA gene, constructed in vitro by fusing fragments of the E. coli chromosomes into a lambdoid bacteriophage. Such phages carry at least two essential genes and are able to suppress both the thermosensitivity and abnormal rifampicin sensitivity associated with the firA200 allele. The finding that some, but not all, of the lambdafirA phages have a temperature dependent growth defect is discussed.

Molecular basis of a control mechanism of DNA synthesis in mammalian cells

Personal observations made on the model of isoproterenol-stimulated DNA synthesis have pointed out the following: 1) cell hypertrophy precedes constantly the onset of DNA synthesis; 2) the length of the G1 phase is mass-dependent; 3) accumulation of ribosomes is needed for cell progress through G1; 4) ribosomal protein synthesis is involved in cell growth activation. These results together with a consideration of the pertinent literature allow us to formulate a hypothesis on the control of cell division in mammalian cells. DNA synthesis might be the terminal event in a chain of metabolic processes whereby a cell adjusts itself to increased functional demands (Increased Functional Demand Hypothesis). The main points of this model are the following: the interaction of the extracellular effector on the target cells first activates the pre-existent protein-synthesizing apparatus of the cell, which in turn brings about the activation of the "translation-transcription connecting mechanism" whereby the cells adjusts itself to an increased need for protein synthesis. Such a mechanism is characterized by cytoplasmic signals arising from the protein-synthesizing apparatus of the cell which reach the nucleus and call forth a messenger RNA for ribosomal proteins. The latter, once synthesized, protect the nascent ribosomal RNA from nuclease attack, resulting in an accumulation of ribosomes in the cytoplasm. Once the ribosomes have reached a "critical amount", the cell is triggered to enter DNA synthesis. As a link between the enhanced ribosomal RNA synthesis and DNA synthesis a reduction in the capacity of the ribonucleotide pool as source of DNA precursors has been suggested.

In vitro synthesis of enzymes of the tryptophan operon of Escherichia coli

A protein fraction, called At (= anti termination) factor, has been isolated from extracts of E. coli and partially purified. The At factor stimulates the synthesis in vitro of anthranilate synthetase, an enzyme encoded by two genes of the tryptophan (trp) operon, but has no effect on the synthesis of T7 RNA polymerase and other T7- and T4 coded proteins. The At factor stimulates the synthesis of trp mRNA; it has no effect on the translation of trp mRNA. We conclude that in vitro transcription of the trp operon is positively controlled.

Purification and properties of D protein: a transcription factor of Escherichia coli

D factor is protein that stimulates DNA transcription in vitro by RNA polymerase. For DNA from bacteriophage lambda, we present evidence that D protein interacts with DNA to increase the frequency and improve the specificity of initiation by RNA polymerase.

Stimulation of RNA synthesis by two protein factors in extracts of Escherichia coli

Two separate protein factors that markedly stimulate DNA-dependent RNA polymerase have been partially purified from ribosome-free extracts of E. coli Q13 cells. These proteins appear to differ from sigma, M, H, psi, and the factor described by Mahadik and Srinivasan. The stimulation by either factor requires the presence of the sigma protein. Using RNA-DNA hybridization competition analyses, we also demonstrate that neither of the new factors preferentially stimulates the synthesis of ribosomal RNA. The purification, properties, and mechanism of action of these new factors are examined.

An inhibitory protein of Escherichia coli RNA polymerase in bacteriophage T3-infected cells (core polymerase-sigma factor-host polymerase-phage polymerase-initiation)

A partially purified protein isolated from bacteriophage T3-infected cells of Escherichia coli B markedly inhibits the activity of E. coli RNA polymerase, slightly inhibits the activity of purified T3 polymerase, and does not inhibit the activity of either core polymerase or the ribosome-bound T3 polymerase. The properties of this protein and its mechanism of action have been studied. It appears to antagonize the action of the sigma factor component of RNA polymerase.