32 research outputs found
Determination of the target nucleosides for members of two families of 16S rRNA methyltransferases that confer resistance to partially overlapping groups of aminoglycoside antibiotics
The 16S ribosomal RNA methyltransferase enzymes that modify nucleosides in the drug binding site to provide self-resistance in aminoglycoside-producing micro-organisms have been proposed to comprise two distinct groups of S-adenosyl-l-methionine (SAM)-dependent RNA enzymes, namely the Kgm and Kam families. Here, the nucleoside methylation sites for three Kgm family methyltransferases, Sgm from Micromonospora zionensis, GrmA from Micromonospora echinospora and Krm from Frankia sp. Ccl3, were experimentally determined as G1405 by MALDI-ToF mass spectrometry. These results significantly extend the list of securely characterized G1405 modifying enzymes and experimentally validate their grouping into a single enzyme family. Heterologous expression of the KamB methyltransferase from Streptoalloteichus tenebrarius experimentally confirmed the requirement for an additional 60 amino acids on the deduced KamB N-terminus to produce an active methyltransferase acting at A1408, as previously suggested by an in silico analysis. Finally, the modifications at G1405 and A1408, were shown to confer partially overlapping but distinct resistance profiles in Escherichia coli. Collectively, these data provide a more secure and systematic basis for classification of new aminoglycoside resistance methyltransferases from producers and pathogenic bacteria on the basis of their sequences and resistance profiles
Videos for embryology teaching, power and weakness of an innovative tool
International audienc
Genome-Wide Signatures of ‘Rearrangement Hotspots’ within Segmental Duplications in Humans
The primary objective of this study was to create a genome-wide high resolution map (i.e., .100 bp) of ‘rearrangement
hotspots’ which can facilitate the identification of regions capable of mediating de novo deletions or duplications in
humans. A hierarchical method was employed to fragment segmental duplications (SDs) into multiple smaller SD units.
Combining an end space free pairwise alignment algorithm with a ‘seed and extend’ approach, we have exhaustively
searched 409 million alignments to detect complex structural rearrangements within the reference-guided assembly of the
NA18507 human genome (186 coverage), including the previously identified novel 4.8 Mb sequence from de novo
assembly within this genome. We have identified 1,963 rearrangement hotspots within SDs which encompass 166 genes
and display an enrichment of duplicated gene nucleotide variants (DNVs). These regions are correlated with increased nonallelic
homologous recombination (NAHR) event frequency which presumably represents the origin of copy number
variations (CNVs) and pathogenic duplications/deletions. Analysis revealed that 20% of the detected hotspots are clustered
within the proximal and distal SD breakpoints flanked by the pathogenic deletions/duplications that have been mapped for
24 NAHR-mediated genomic disorders. FISH Validation of selected complex regions revealed 94% concordance with in silico
localization of the highly homologous derivatives. Other results from this study indicate that intra-chromosomal
recombination is enhanced in genic compared with agenic duplicated regions, and that gene desert regions comprising SDs
may represent reservoirs for creation of novel genes. The generation of genome-wide signatures of ‘rearrangement
hotspots’, which likely serve as templates for NAHR, may provide a powerful approach towards understanding the
underlying mutational mechanism(s) for development of constitutional and acquired diseases