Ein genetischer Beitrag zur Frage der Spätform der Pelizaeus-Merzbacherschen Krankheit

Ohne ZusammenfassungMit 6 Textabbildungen     

A five-nucleotide sequence protects DNA from exonucleolytic degradation by AddAB, the RecBCD analogue of Bacillus subtilis

Homologous recombination in Bacillus subtilis requires the product of the addA and addB genes, the AddAB enzyme. This enzyme, which is both a helicase and a powerful nuclease, is thought to be the counterpart of the Escherichia coli RecBCD enzyme. From this analogy, it is expected that the nuclease activity of AddAB can be downregulated by a specific DNA sequence, which would correspond to the chi site in E. coli . Using protection of linear double-stranded DNA as a criterion, we identified the five-nucleotide sequence 5'-AGCGG-3', or its complement 5'-CCGCT-3', as being sufficient for AddAB nuclease attenuation. We have shown further that this attenuation occurs only if the sequence is properly oriented with respect to the translocating AddAB enzyme. Finally, inspection of the complete B. subtilis genome revealed that this five-nucleotide sequence is over-represented and is, in a majority of cases, co-oriented with DNA replication. Based on these observations, we propose that 5'-AGCGG-3', or its complement, is the B. subtilis analogue of the E. coli chi sequence.     

In vitro movement of human embryonic fibroblasts with normal and anomalous sets of chromosomes

Migration of diploid postnatal and embryonic diploid and aneuploid cells was studied using a modified method of investigation of leukocyte migration under agarose. The method permits to study migration of fibroblasts and other proliferating cells. Embryonic fibroblasts were shown to move faster, than postnatal fibroblasts. Cells with trisomy 7, 9 and C, and triploid cells were found to move slower than diploid cells. Locomotor disturbances are supposed to be the basis of impairment of morphogenesis in chromosomal anomalies in man.     

Best practices for the visualization,mapping, and manipulation of R‐loops

R‐loops represent an abundant class of large non‐B DNA structures in genomes. Even though they form transiently and at modest frequencies, interfering with R‐loop formation or dissolution has significant impacts on genome stability. Addressing the mechanism(s) of R‐loop‐mediated genome destabilization requires a precise characterization of their distribution in genomes. A number of independent methods have been developed to visualize and map R‐loops, but their results are at times discordant, leading to confusion. Here, we review the main existing methodologies for R‐loop mapping and assess their limitations as well as the robustness of existing datasets. We offer a set of best practices to improve the reproducibility of maps, hoping that such guidelines could be useful for authors and referees alike. Finally, we propose a possible resolution for the apparent contradictions in R‐loop mapping outcomes between antibody‐based and RNase H1‐based mapping approaches.     

How long is too long? Effects of loop size on G-quadruplex stability

We compared here 80 different sequences containing four tracts of three guanines with loops of variable length (between 1 and 15 bases for unmodified sequences, up to 30 for fluorescently labeled oligonucleotides). All sequences were capable of forming stable quadruplexes, with T_m above physiological temperature in most cases. Unsurprisingly, the melting temperature was systematically lower in sodium than in potassium but the difference between both ionic conditions varied between 1 and >39°C (average difference: 18.3°C). Depending on the sequence context, and especially for G4 sequences involving two very short loops, the third one may be very long without compromising the stability of the quadruplex. A strong inverse correlation between total loop length and T_m was found in K⁺: each added base leads to a 2°C drop in T_m or ∼0.3 kcal/mol loss in ΔG°. The trend was less clear in Na⁺, with a longer than expected optimal loop length (up to 5 nt). This study will therefore extend the sequence repertoire of quadruplex-prone sequences, arguing for a modification of the widely used consensus (maximal loop size of 7 bases).     

The clinical significance of HAMA in patients treated with mouse monoclonal antibodies.

Twenty-four patients were analyzed for the development of HAMA (human antimouse antibodies) after being treated with repeated doses (200-500 mg) of the mouse monoclonal antibody (MAb) 17-1A. All patients developed anti-17-1A IgG antibodies, and most of them also developed IgM antibodies. In only two patients could immune complexes be demonstrated. Allergic reactions were rare (1.9%). In an extended study, a further 19 patient were analyzed for an idiotypic response. Forty-one out of 43 patients developed antiidiotypic antibodies (ab2), and 20 of these also anti-anti-idiotypic antibodies (ab3). Ab3+ patients responded significantly better (p = 0.01) and survived longer (p < 0.001) compared to ab3- patients. In this study, we showed that MAb 17-1A could be repeatedly given on a safe basis. The development of high titers of HAMA did not cause significant clinical problems when further repeated infusions of MAb 17-1A were given. The development of an idiotypic response also indicate that the induction of HAMA might be beneficial and not harmful to the patient.