Regulation Of Eukaryotic Gene Expression Research Articles

Nucleocytoplasmic RNA transport.

During the past decade, it has become evident that, in eukaryotes, RNA molecules undergo a complex series of chemical modifications after transcription and before translation and that some of these modifications coincide with alterations in subcellular distribution. There is growing evidence that these posttranscriptional events, both at the level of the RNA molecule (“processing”) and at the whole-cell level (“transport”), are of great biological importance. Posttranscriptional RNA processing has been thoroughly and frequently reviewed over the past few years, and (although many controversies remain to be resolved) a coherent body of thought has existed in the field at least since publication of the review by Perry (1976). However, RNA transport, the cellbiological counterpart of processing, has been much less thoroughly reviewed, and despite the steady accumulation of experimental data, the field lacks a coherent body of thought. The review by Webb et al. (1981) is comprehensive and argues cogently for a special messenger RNA (mRNA) transport mechanism, susceptible to regulating influences including hormones, and for abnormalities at the locus of RNA transport in a number of pathological conditions. As the first complete survey of the field, however, it offers no general hypothesis about mechanism. An article on the cytoplasmic regulation of eukaryotic gene expression by Lichtenstein et al. (1981) contains much that is relevant to RNA transport, but, being concerned with the assessment of an interesting speculative model, does not address itself critically to the experimental basis of the data to which it refers.

Allosteric stimulatory effect of S-adenosylmethionine on the RNA polymerase in cytoplasmic polyhedrosis virus. A model for the positive control of eukaryotic transcription.

The stimulatory effect of S-adenosylmethionine (AdoMet) on cytoplasmic polyhedrosis virus transcription in vitro has been studied in detail. AdoMet affects the initiation of transcription but not chain elongation. It is required for each reinitiation step during multiple transcription cycles. Under limited conditions of synthesis in reaction mixtures depleted of UTP and CTP, a greater amount of initiator oligonucleotides was formed in the presence of AdoMet than in its absence. These small oligonucleotides were also formed along with the completed mRNA under conditions of mRNA formation. Although these capped (or uncapped) oligonucleotides corresponded to the 5'-terminal sequence of cytoplasmic polyhedrosis virus mRNA, they failed to substitute for AdoMet in promoting mRNA synthesis. Efficient synthesis of mRNA containing 5'-m7GpppAmpG was dependent on the concentrations of AdoMet and the initiating nucleotide, ATP. There was also an inverse relationship between AdoMet and ATP concentrations such that the apparent Km for ATP was decreased strikingly from 10 to 0.25 mM as the AdoMet concentration was increased from 5 to 500 microM. This effect was observed only for ATP. Double reciprocal plots for estimating the Km of ATP formed concave upward curves but became linear upon addition of a higher concentration of AdoMet, indicating a positive cooperativity of ATP and allosteric effect of AdoMet in the initiation process. Stimulation of transcription by lowering the Km for the initiating nucleotide at the promoter site is proposed as a model for positive regulation of eukaryotic gene expression.

Separation of a stimulatory factor of RNA polymerase II from protein kinase activity of ehrlich ascites tumor cells

The regulation of eukaryotic gene expression is one of the most exciting problems in modern biology. Since Roeder and Rutter reported the multiple forms of eukaryotic RNA polymerase [l] , extensive studies have been done on the purification of these enzymes. Along with the purification of the enzymes, there have been many papers reporting the factors stimulating these enzymes, especially RNA polymerase II [2-61. These factors are expected to play important roles in the regulation of eukaryotic transcription. In order to elucidate the function of these factors, we purified one of these factors, named S-II, from Ehrlich ascites tumor cells [7] . This factor is a basic protein having molecular weight of 38 000 and stimulates only RNA polymerase II and distinctly insensitive to RNA polymerase I. The stimulation cannot be detected when poly [d(A-T) is used as template under the conditions where more than tenfold stimulation is obtained with homologous DNA as template. Recently, Dahmus showed that a stimulatory factor of RNA polymerase II from Novikoff hepatoma cells, named HLF2, contained protein kinase activity [8] . He proposed that phosphorylation of RNA polymerase II by this factor was required for the subsequent stimulation of RNA synthesis. In this paper we report results showing that S-II could not be copuritied with protein kinase and that protein kinase activity was not essential for the stimulation of RNA polymerase II. 2. Methods