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Heme biosynthesis is a highly conserved pathway which is present in all kingdoms, from Archaea to higher organisms such as plants and mammals. The heme molecule acts as a prosthetic group for different proteins and enzymes involved in energy metabolism and reactions involved in electron transfer. Based on our recent findings and other recent reports, we here illustrate that heme is more than a co-factor. We also discuss the necessity to gain more insight into the heme biosynthesis pathway regulation, as this interacts closely with overall stress control. Understanding heme biosynthesis and its regulation could impact our ability to develop more efficient yeast cell factories for heterologous protein production.

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Pityriasis rubra pilaris (PRP) is a rare group of hyperkeratotic, papulosquamous diseases that can be acquired or inherited. Cases of PRP associated with malignancy have been rarely reported. We report a case of 46-year-old man who presented with rapidly progressing PRP as a possible initial cutaneous symptom of a previously undiagnosed laryngeal carcinoma. Microlaryngoscopy was performed because of the patient's hoarseness, and this revealed leucoplakia on the left vocal cord. Histopathological examination led to the diagnosis of squamous cell carcinoma in situ. After surgical treatment, the clinical signs of PRP began to resolve, and the patient was free of skin lesions at follow-up. This case represents a rare coexistence of PRP with malignancy, and indicates that PRP can occur as paraneoplastic dermatosis associated with laryngeal cancer.

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A 37-year-old male patient presented with a Bellini duct carcinoma, at first as a metastatic illness of the paraaortal lymph nodes, without significant radiologic signs of a kidney tumor. Cytological diagnostics did not recognize this tumor. Macroscopically and microscopically the tumor fulfilled the major and minor criteria of Sringly et al., but immunohistochemical findings did not show cell affinity for UEA-1, which, according to the literature, typically confirms its origin from Bellini ducts. This rare neoplasm, primarily found in a younger population, still represents a diagnostic and therapeutical challenge as a result of its aggressive clinical course. In our patient, as in the majority of cases presented in the literature, tumor prognosis was very poor, in spite of aggressive surgical, radium and immune therapy.

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The article is a longitudinal review of experimental research of high didactic systems effects in history teaching over the last 30 years. The aims of research are to evaluate: 1. position of adolescent, especially neurotic pupils in the teaching process; 2. possibilities to enhance the level of restructured matter (historical anthropology) in programmed and problem-solving teaching; 3. influence on the anxiety, attitudes and success of pupils with changes in the teaching process. Authors conclude, that the teaching process can influence the emotional state of the neurotic pupil. Higher didactic systems in a short time can influence the enhanced level of knowledge in relation to the traditional teaching systems. In the new systems, the attitudes of the pupils towards the teaching can change positively. Experiments carried out point to the possibility of changes of national identity and the necessity of an anthropological approach to reform the educational system.

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Some phages survive irradiation much better upon multiple than upon single infection, a phenomenon known as multiplicity reactivation (MR). Long ago MR of UV-irradiated lambda red phage in E. coli cells was shown to be a manifestation of recA-dependent recombinational DNA repair. We used this experimental model to assess the influence of helicase II on the type of recombinational repair responsible for MR. Since helicase II is encoded by the SOS-inducible uvrD gene, SOS-inducing treatments such as irradiating recA(+) or heating recA441 cells were used. We found: i) that MR was abolished by the SOS-inducing treatments; ii) that in uvrD background these treatments did not affect MR; and iii) that the presence of a high-copy plasmid vector carrying the uvrD(+) allele together with its natural promoter region was sufficient to block MR. From these results we infer that helicase II is able to antagonize the type of recA-dependent recombinational repair acting on multiple copies of UV-damaged lambda DNA and that its anti-recombinogenic activity is operative at elevated levels only.

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RecBCD enzyme is involved in the radiation-induced process known as prophage inactivation. The process leads to the inability of lambda prophage to excise itself from the Escherichia coli chromosome via site-specific recombination. In this work we sought to further characterize the role of RecBCD enzyme in this process. In addition, we examined the ability of irradiated prophage to recombine with the infecting homologous phage. We used several E. coli mutants differentially altered in RecBCD's activities. The results showed that in the mutants carrying either recB2109 or recD1903, which do not exhibit significant nuclease activities, the prophage progressively loses its capacity for both site-specific and general recombination. In the recB268 null mutant, however, prophage recombinogenicity remained fully preserved. We also showed that the prophage unable to recombine retained its ability to complement the mutant infecting phage and that the recombination frequencies in phage x phage crosses were not affected by postirradiation incubation. Our results suggest that the helicase activity of RecBCD is responsible for the progressive loss of prophage recombinogenicity. This loss is most probably a consequence of the unsuccessful RecBCD-dependent recombinational repair of double-stranded breaks in the cell chromosome, during which some structures unsuitable for further recombination reactions may be produced.

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The RuvC protein is important for DNA recombination and repair in Escherichia coli. The present work shows that a ruvC null mutation introduced into a recBC sbcBC background causes severe defects in chromosome segregation and cell division. Both defects were found to result from abortive recombination initiated by the RecA protein.

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The mechanism of DNA replication in ultraviolet (UV)-irradiated Escherichia coli is proposed. Immediately after UV exposure, the replisome aided by single-strand DNA-binding protein (SSB) can proceed past UV-induced pyrimidine dimers without insertion of nucleotides. Polymerisation eventually resumes somewhere downstream of the dimer sites. Due to the limited supply of SSB, only a few dimers can be bypassed in this way. Nevertheless, this early DNA synthesis is of great biological importance because it generates single-stranded DNA regions. Single-stranded DNA can bind and activate RecA protein, thus leading to induction of the SOS response. During the SOS response, the cellular level of RecA protein increases dramatically. Due to the simultaneous increase in the concentration of ATP, RecA protein achieves the high-affinity state for single-stranded DNA. Therefore it is able to displace DNA-bound SSB. The cycling of SSB on and off DNA enables the replisome to bypass a large number of dimers at late post-UV times. During this late replication, the stoichiometric amounts of RecA protein needed for recombination are involved in the process of postreplication repair.

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DNAs from phage mutants M13mp18 and M13mp18/MP-1 were used to construct two closed circular heteroduplexes. One of them carried the sequence 5'-CCTGGG-3' 3'-GGGCCC-5' with a T.G mismatch at the position 6248. The other carried the sequence 5'-CCCGGG-3' 3'-GGACCC-5' with a C.A mismatch at the same position. Heteroduplexes were exposed to 7 restriction endonucleases having recognition sites within the sequence 5'-CCCGGG-3' 3'-GGGCCC-5' and to 1 restriction endonuclease having a recognition site within the sequence 5'-CCTGGG-3' 3'-GGACCC-5'. All tested enzymes cleaved at least one mismatch-containing sequence although with reduced efficiency. Smal and Xmal tolerated both mismatch-containing sequences. Aval, Hpall, Mspl, Ncil and Nsplll were able to tolerate only the T.G containing sequence, while BstNl was able to tolerate only the C.A containing sequence. It is inferred that the tolerance displayed by Smal and Xmal depends on the presence of either the original purines or the original pyrimidines in mismatches of both the T.G and C.A type and that all other tested enzymes require the presence of the original purines in mismaches of both types.

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By making use of the temperature-sensitive mutant recB270, we showed that the RecBCD enzyme is needed for repair between 1 and 4 h after UV exposure. recB-dependent prophage inactivation (Petranovic et al. (1984), Mol. Gen. Genet., 196, 167-169) takes place in all dying cells during the same period of time. The kinetics of decrease in the yield of recombinants in phage-propage crosses resemble those of prophage inactivation in UV-irradiated bacteria. This indicates that recombination processes (including site-specific recombination required for prophage excision) are blocked in cells destined to die. On the basis of our results, we suggest that a large fraction of damaged cells is rescued by the RecA-RecBCD recombination pathway. If repair is unsuccessful, RecA-RecBCD recombination intermediates persist in the irradiated cells leading to prophage inactivation.

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DNA degradation in Escherichia coli uvrA recA bacteria exposed to a low dose (0.07 J/m2) of ultraviolet radiation was studied. A considerable amount of the newly-synthesized DNA, which contains gaps opposite pyrimidine dimers, is broken down. In contrast, parental, dimer-containing DNA is resistant to radiation-induced degradation.

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The lysogenization of ultraviolet-irradiated Escherichia coli cells by the lambda phage was studied. Genetic analysis indicates that changes in the number of the lysogenized cell during post-UV growth is primarily due to the change in the proteolytic activity of RecA protein. Full proteolytic activity is achieved only in the presence of the functional recB gene product.

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If ultraviolet irradiated, lambda-lysogenic Escherichia coli K12 bacteria are incubated for 4 to 6 h at 30 degrees C, lambda prophage becomes inactive in the non-surviving cells. This was demonstrated by the use of lambda cIts857ind1 prophage which can be induced by heat but not by ultraviolet light. An analysis with various bacterial mutants showed that RecBC recombination enzyme is required in conjunction with RecA protein for prophage inactivation.

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Post-UV DNA synthesis in Escherichia coli uvrA recA cells was studied. A low dose of UV radiation (0.07 J/m2), which caused no degradation of the dimer-containing DNA, was used. This enabled us to make a direct comparison between DNA synthesis on the normal template and DNA synthesis on the UV-damaged template. There was no change in the post-UV DNA synthesis kinetics during the first 60 min of post-irradiation incubation. A reduced rate of DNA synthesis was observed at later post-UV times when the dimers are expected to have passed through the normal replication complex. This reduced rate of DNA synthesis was associated with loss of the biological activity of the DNA. We suggest that the gaps opposite dimers rather than dimers per se interfere with normal replication, thus leading to cell death of uvrA recA bacteria.

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Deoxyribonucleic acid synthesis after ultraviolet irradiation was studied in wild-type, uvrA, recB, recA recB, and recA Escherichia coli strains. Inhibition of deoxyribonucleic acid synthesis, which occurs almost immediately after exposing the cells to ultraviolet radiation, depends on the functional gene recA.

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The fate of the prophage part of the lysogenic chromosome was followed in the course of post-ultraviolet incubation. For this purpose, lambda cI857 ind prophage, which can be induced by heat but not by ultraviolet light, was used. The prophage, intially more resistant than its repair-proficient host cell, was rapidly inactivated. This inactivation was not caused by the impaired capacity of irradiated cells to support growth of the phage. Over the entire dose range tested, little, if any, sensitivity difference between the host and the prophage was found at the end of cell division delay. Rapid inactivation of the prophage was also observed in uvr cells after small doses of ultraviolet light. The same small doses did not cause inactivation in lysogens carrying a mutation in the gene recA. This suggests that the functional gene recA is required for inactivation of the prophage part of the lysogenic chromosome.

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