All eukaryotic cells, including African trypanosomes, require iron for growth and division, and this iron is acquired by the receptor-mediated endocytosis of iron-loaded transferrin (diFe(3+)-transferrin). In trypanosomes transferrin (Tf) has been shown to be delivered into lysosomes and may not recycle back to the cell surface as it does in mammalian cells (Grab, D. J., et al., Eur. J. Cell Biol. 59, 398-404 (1992)). Here, we describe for the first time, the characteristics of a Tf-binding protein with receptor-like properties in Trypanosoma brucei brucei. Bloodstream forms of rodent-adapted T. brucei were incubated with [35S]methionine and detergent lysates chromatographed on a Sephacryl S-300 column. Fractions were incubated with anti-Tf serum to immunoprecipitate Tf/Tf-binding protein complexes. On sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) the molecular mass of the major protein in the immunoprecipitate was 88 to 92 kDa. Tf-binding proteins could also be isolated using diferric Tf-Sepharose. The molecular mass of the major Tf-binding protein, as estimated from Sephacryl S-300 column chromatography, in the presence of detergent, was approximately 90 to 100 kDa and 90 kDa with SDS-PAGE. Each 90 kDa Tf-binding protein was able to bind one molecule of diferric Tf. Since monoclonal antibodies to human and bovine Tf receptors failed to react with any trypanosome proteins, antisera were raised against the T. brucei Tf-binding proteins eluted from Tf-Sepharose at low pH. These antibodies recognized a 90 kDa protein on Western blots of a T. brucei lysate and inhibited the growth of T. brucei in vitro. Immunolocalization studies, using this antiserum showed that the Tf-binding protein was localized in the flagellar pocket and within the early endosomal compartments. In the presence of protease inhibitors there was additional localization in lysosome-like organelles. The Tf-binding characteristics and localization of this 90 kDa protein suggest that this molecule is a strong candidate as a physiological receptor for Tf in these parasites.
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Nucleic Acids Res
January 2025
Department of Genome Sciences, University of Virginia, PO Box 800717, Charlottesville, VA 22908, USA.
Many transcription factors (TFs) have been shown to bind to super-enhancers, forming transcriptional condensates to activate transcription in various cellular systems. However, the genomic and epigenomic determinants of phase-separated transcriptional condensate formation remain poorly understood. Questions regarding which TFs tend to associate with transcriptional condensates and what factors influence their association are largely unanswered.
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January 2025
National Agri-Food Biotechnology Institute, Knowledge City, Mohali, Punjab, India. Electronic address:
Nuclear protein transcription factors (TFs) regulate all biological processes in plants and are necessary for gene regulation. The transcription of genes during plant growth and development and their response to environmental cues are regulated by TF binding to specific promoter regions in the genomic DNA. Polyploid plants with several sets of chromosomes frequently display intricate genomic biases concerning TF expression.
View Article and Find Full Text PDFBMC Genomics
January 2025
International Institute of Molecular and Cell Biology in Warsaw, Laboratory of Zebrafish Developmental Genomics, Księcia Trojdena 4, Warsaw, 02-109, Poland.
Congenital heart disease (CHD) is a prevalent condition characterized by defective heart development, causing premature death and stillbirths among infants. Genome-wide association studies (GWASs) have provided insights into the role of genetic variants in CHD pathogenesis through the identification of a comprehensive set of single-nucleotide polymorphisms (SNPs). Notably, 90-95% of these variants reside in the noncoding genome, complicating the understanding of their underlying mechanisms.
View Article and Find Full Text PDFNat Commun
January 2025
Science for Life Laboratory, Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden.
The rate at which transcription factors (TFs) bind their cognate sites has long been assumed to be limited by diffusion, and thus independent of binding site sequence. Here, we systematically test this assumption using cell-to-cell variability in gene expression as a window into the in vivo association and dissociation kinetics of the model transcription factor LacI. Using a stochastic model of the relationship between gene expression variability and binding kinetics, we performed single-cell gene expression measurements to infer association and dissociation rates for a set of 35 different LacI binding sites.
View Article and Find Full Text PDFbioRxiv
January 2025
Division of Hematology and Medical Oncology, Department of Medicine and Meyer Cancer Center, Weill Cornell Medicine, New York, NY, USA.
Gene expression is coordinated by a multitude of transcription factors (TFs), whose binding to the genome is directed through multiple interconnected epigenetic signals, including chromatin accessibility and histone modifications. These complex networks have been shown to be disrupted during aging, disease, and cancer. However, profiling these networks across diverse cell types and states has been limited due to the technical constraints of existing methods for mapping DNA:Protein interactions in single cells.
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