A nuclease hypersensitive element in the human c-myc promoter adopts several distinct i-tetraplex structures.

Nucleic acid structure-function correlations are pivotal to major biological events like transcription, replication, and recombination. Depending on intracellular conditions in vivo and buffer composition in vitro, DNA appears capable of inexhaustible structure variation. At moderately acidic, or even neutral pH, DNA strands that are rich in cytosine bases can associate both inter- and intramolecularly to form i-tetraplexes. The hemiprotonated cytosine(+)-cytosine base pair constitutes the building block for the formation of i-tetraplexes, and motifs for their formation are frequent in vertebrate genomes. A major control element upstream of the human c-myc gene, which has been shown to interact sequence specifically with several transcription factors, becomes hypersensitive to nucleases upon c-myc expression. The control element is asymmetric inasmuch as that one strand is uncommonly rich in cytosines and exhibits multiple motifs for the formation of i-tetraplexes. To investigate the propensity for their formation we employ circular dichroism (CD) in combination with ultra violet (UV) spectroscopy and native gel electrophoresis. Our results demonstrate the cooperative formation of well-defined i-tetraplex structures. We conclude that i-tetraplex formation occurs in the promoter region of the human c-myc gene in vitro, and discuss implications of possible biological roles for i-tetraplex structures in vivo. Hypothetical formation of intramolecular fold-back i-tetraplexes is important to c-myc transcription, whereas chromosomal translocation events might involve the formation of bimolecular i-tetraplex structures.

[Chlamydia trachomatis in men with impaired fertility]. / Chlamydia trachomatis u muzu s poruchou plodnosti.

OBJECTIVE: The objective of the prospective study was to assess whether there exists a relationship between the results of positive laboratory tests for the presence of Chlamydia infection (assessment of the presence of Chlamydia trachomatis in the ejaculate by the DNA amplification method, IgA and IgG antichlamydia antibodies in the ejaculate and serum), an abnormal spermiogram and total number of sexual partners in men from infertile couples examined at the Gynaecological and Obstetric Clinic of the First Medical Faculty, Charles University Prague. DESIGN: Prospective clinical study. SETTING: Department of Gynaec.-Obstet., the 1st Medical Faculty of the Charles University, Prague, Czech Republic--Institut of Clinical Biochemy, the 1st Medical Faculty of Charles University, Prague, Czech Republic. METHOD: 101 men were examined. In all the spermiogram was evaluated according to WHO criteria. Specific antichlamydial antibodies IgA and IgG is serum and the ejaculate were assessed by the ELISA method. Evidence of the DNA portion of Chlamydia trachomatis was provided by the MEIA method. Amplification of DNA by LCR was made on a Thermocycler. By means of an aimed questionnaire the number of all sexual partners was assessed. The men were divided into three groups with 1-5, 6-9 and with 10 or more partners. Patients where Chlamydia infection was detected were treated with Ig Azitromycin and their spermiogram was checked 6-8 weeks after treatment. The results of the examination were tested by the chi square test. RESULTS: An abnormal spermiogram was found in 44 (44%) of the examined subjects. With the increasing number of sexual partners the number of men with pathospermia increased. In none LCR for the presence of Chlamydia trachomatis was positive in the ejaculate. In 15 examined patients IgA antichlamydia antibodies were found in the ejaculate. At the same time in all an abnormal spermiogram was found and 11 (73%) of them had six or more sexual partners. After treatment in 8 (62%) of 13 (two did not attend the check-up) marked improvement of the spermiogram occurred. CONCLUSION: IgA antichlamydial antibodies in the ejaculate proved in 62% of the examined men with an abnormal spermiogram a useful indicator of infection in the genital tract. With the increasing number of sexual partners the number of pathospermias increased.