The phosphorylation of the RNA polymerase II (RNAP II) carboxy-terminal domain (CTD) plays a key role in mRNA metabolism. The relative ratio of hyperphosphorylated RNAP II to hypophosphorylated RNAP II is determined by a dynamic equilibrium between CTD kinases and CTD phosphatase(s). The CTD is heavily phosphorylated in meiotic Xenopus laevis oocytes. In this report we show that the CTD undergoes fast and massive dephosphorylation upon fertilization. A cDNA was cloned and shown to code for a full-length xFCP1, the Xenopus orthologue of the FCP1 CTD phosphatases in humans and Saccharomyces cerevisiae. Two critical residues in the catalytic site were identified. CTD phosphatase activity was observed in extracts prepared from Xenopus eggs and cells and was shown to be entirely attributable to xFCP1. The CTD dephosphorylation triggered by fertilization was reproduced upon calcium activation of cytostatic factor-arrested egg extracts. Using immunodepleted extracts, we showed that this dephosphorylation is due to xFCP1. Although transcription does not occur at this stage, phosphorylation appears as a highly dynamic process involving the antagonist action of Xp42 mitogen-activated protein kinase and FCP1 phosphatase. This is the first report that free RNAP II is a substrate for FCP1 in vivo, independent from a transcription cycle.In many metazoans, early development is characterized by major changes in the global transcriptional activity of the zygote (13). After fertilization, development proceeds for a while in the absence of transcription and is dependent on the translation of maternal mRNAs stored during ovogenesis. Transcription resumes at a stage which is species specific and corresponds to the two-cell stage in mice. In Xenopus laevis, transcription resumes at the 12th cleavage division at a major developmental transition known as the midblastula transition. Important changes in RNA polymerase II (RNAP II) phosphorylation have been described to occur in worm (27), fly (20), mammalian (3), and amphibian (25) embryos during this period.RNAP II phosphorylation is a key event in the transcription cycle (11, 12). The largest subunit of RNAP II (Rpb1) can be extensively phosphorylated on its carboxy-terminal domain (CTD), which is comprised of up to 52 repeats of the consensus heptapeptide Tyr-Ser-Pro-Thr-Ser-Pro-Ser. Thus, in somatic cells, two forms of RNAP II coexist in a dynamic equilibrium (15). The hypophosphorylated IIA form assembles into preinitiation complexes, whereas the hyperphosphorylated IIO form catalyzes transcript elongation and facilitates the recruitment of the pre-mRNA processing machinery. CTD dephosphorylation is required to recycle the polymerase at the end of each round of transcription.Several CTD kinases have been identified (for reviews, see references 5, 21, and 28): the CDK8 subunit of the mediator complex in the RNAP II holoenzyme, the CDK7 subunit of the general transcription factor TFIIH which assembles in the preinitiation complex, the CDK9 subunit of P-TEFb (positive transcription el...

Analysis of the stress response of closely related rat hepatoma clones revealed that the major inducible heat-shock protein 68 (HSP68) was only slightly inducible upon stress in the glucocorticoidresistant, dedifferentiated clone-2 cells, but strongly activated in the differentiated, glucocorticoidsensitive Faza 967 cells from which clone 2 was derived. The decreased inducibility of HSP68 in clone-2 cells was not the consequence of altered kinetics of protein synthesis recovery, was not correlated with the deficient inducibility of other major heat-shock proteins and had no effect on the heat sensitivity of the cells. This deficiency was observed after treatment with mild and strong heat and various chemicals. The results of nuclear run-on experiments suggested that the impairment of HSP68 mRNA induction most likely occurs at the transcriptional level and is probably specific for the corresponding gene. In Faza 967 and clone-2 cells, stress activated comparable levels of heat-shockfactor binding to the heat-shock element, and the expression of a reporter gene under the control of murine HSP70.1 promoter was strongly stimulated in both cells. Therefore, our results raise the possibility that the deficient stress inducibility of HSP68 is due to some specific regulation of the endogeneous HSP68 gene, rather than to a deficiency of the heat-shock factor or mutation of the corresponding gene, In response to heat shock and exposure to various chemicals, the transcription of a small set of genes, the heat-shock genes, is specifically activated in most cells. This activation results in the vigorous synthesis of several heat-shock proteins (HSP) (for a review, see [l]). The major HSP display essential functions in unstressed cells, related to protein folding and unfolding, such as chaperoning unfolded protein precursors, assisting translocation across membranes, multiprotein assembly and protein degradation. During heat shock and other stresses, several proteins are denatured and HSPs are thought to prevent protein aggregation, to help recovery from denaturation and to assist in the degradation of denatured proteins (for reviews see [l -31).The synthesis of HSP is regulated at both the transcriptional and post-transcriptional levels (for reviews see [4, 51). Repeats of the GAA-TTC-DNA motif constitute the heatshock elements (HSE) of eukaryotic heat-shock genes and confer the stress inducibility of transcription [l, 61. Stress promotes the HSE binding of the heat-shock transcription factor(s) (HSF) [7]. Although the HSF plays an essential role in transcriptional regulation of the stress genes, the binding of HSF to the HSE does not appear to be sufficient for transcriptional activation [8, 91. Correspondence to A. Venetianer, Institute of Genetics, Biological Research Center, Hungarian Academy of Sciences, Temesvari Str. 62, H-6726 Szeged, HungaryAbbreviations. HSP, heat-shock protein; HSE, heat-shock element; HSF, heat-shock factor.Enzyme. Glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1 .I 2) Post-transcriptional r...

Interferon (IFN) is not able to induce heat-shock protein (HSP) synthesis. However IFN pretreatment of mouse L cells has been shown to enhance the decrease of overall protein synthesis which follows a heat shock, and to stimulate the accumulation of HSPs. We show here that the synthesis of a protein (the hepatitis B virus surface antigen) under the control of a Drosophila HSP 70 promoter is also stimulated in IFN-pretreated cells. The regulation by IFN takes place at two levels: first, the rate of HSP gene transcription is increased in nuclei isolated from IFN-treated cells; second, the synthesis of HSPs is prolonged after pretreatment with IFN. Experiments performed in the presence of actinomycin D show that this effect is due to a stabilization by IFN of mRNAs coding for HSPs.

Comparative studies between two measles virus strains isolated from patients with subacute sclerosing panencephalitis (SSPE) and a prototype low tissue culture passage Edmonston measles virus are described. Differences were noted in several properties. The findings described in this report suggest that strains of measles virus associated with SSPE have different biological properties and apparently cannot be distinguished from laboratory and field strains of the virus.