Howard Hughes Medical Institute

About: Howard Hughes Medical Institute is a nonprofit organization based out in Chevy Chase, Maryland, United States. It is known for research contribution in the topics: Gene & RNA. The organization has 20371 authors who have published 34677 publications receiving 5247143 citations. The organization is also known as: HHMI & hhmi.org.

Single-cell proteomic analysis of S. cerevisiae reveals the architecture of biological noise

Abstract: A major goal of biology is to provide a quantitative description of cellular behaviour. This task, however, has been hampered by the difficulty in measuring protein abundances and their variation. Here we present a strategy that pairs high-throughput flow cytometry and a library of GFP-tagged yeast strains to monitor rapidly and precisely protein levels at single-cell resolution. Bulk protein abundance measurements of >2,500 proteins in rich and minimal media provide a detailed view of the cellular response to these conditions, and capture many changes not observed by DNA microarray analyses. Our single-cell data argue that noise in protein expression is dominated by the stochastic production/destruction of messenger RNAs. Beyond this global trend, there are dramatic protein-specific differences in noise that are strongly correlated with a protein's mode of transcription and its function. For example, proteins that respond to environmental changes are noisy whereas those involved in protein synthesis are quiet. Thus, these studies reveal a remarkable structure to biological noise and suggest that protein noise levels have been selected to reflect the costs and potential benefits of this variation.

Requirement of transcription factor PU.1 in the development of multiple hematopoietic lineages

Abstract: The transcription factor PU.1 is a hematopoietic-specific member of the ets family. Mice carrying a mutation in the PU.1 locus were generated by gene targeting. Homozygous mutant embryos died at a late gestational stage. Mutant embryos produced normal numbers of megakaryocytes and erythroid progenitors, but some showed an impairment of erythroblast maturation. An invariant consequence of the mutation was a multilineage defect in the generation of progenitors for B and T lymphocytes, monocytes, and granulocytes. Thus, the developmental programs of lymphoid and myeloid lineages require a common genetic function likely acting at the level of a multipotential progenitor.

Emergence of Resistant Human Immunodeficiency Virus Type 1 in Patients Receiving Fusion Inhibitor (T-20) Monotherapy

Abstract: The synthetic peptide T-20 (enfuvirtide) represents the first of a new class of antiretroviral compounds to demonstrate in vivo potency by targeting a step in viral entry. T-20 inhibits a conformational change in the human immunodeficiency virus type 1 (HIV-1) transmembrane glycoprotein (gp41) that is required for fusion between HIV-1 and target cell membranes. The initial phase I clinical trial of T-20 treatment for HIV-infected patients thus provided a unique opportunity to evaluate the emergence of resistant virus in vivo to this novel class of antiretroviral agents. All four patients who received an intermediate dose of T-20 (30 mg twice daily) had an initial decline in plasma viral load over the first 10 days but a rising trend by day 14, suggestive of selection for resistant virus. Plasma virus derived from patients enrolled in all dosage groups of the phase I T-20 trial was analyzed by population sequencing before and after treatment. While no mutations were found within a highly conserved 3-amino-acid sequence (GIV) known to be critical for fusion at baseline, after 14 days of therapy, virus from one patient in the 30-mg dose group (30-1) developed a mutation in this motif, specifically an aspartic acid (D) substitution for glycine (G) at position 36. Multiple env clones were derived from the plasma virus of all four patients in the 30-mg dosage group. Sequence analysis of 49 clones derived from the plasma of patient 30-1 on day 14 revealed that 25 clones contained the G36D mutation, while 8 contained the V38A mutation. Dual mutations involving G36D and other residues within the HR1 domain were also identified. In 5 of the 49 env clones, other mutations involving residues 32 (Q32R or Q32H) and 39 (Q39R) were found in combination with G36D. Cloned env sequences derived from the plasma virus of subject 30-3 also had single mutations in the GIV sequence (V38M and I37V) detectable following therapy with T-20. The plasma virus from subjects 30-2 and 30-4 did not contain changes within the GIV sequence. To analyze the biological resistance properties of these mutations, we developed a novel single-cycle HIV-1 entry assay using JC53BL cells which express beta-galactosidase and luciferase under control of the HIV-1 long terminal repeat. Full-length env clones were derived from the plasma virus of patients 30-1 and 30-3 and used to generate pseudotyped virus stocks. The mean 50% inhibition concentrations (IC(50)s) for mutants G36D and V38A (patient 30-1) were 2.3 microg/ml and 11.2 microg/ml, respectively, statistically significant increases of 9.1- and 45-fold, respectively, compared with those of wild-type Env. The IC(50) for the V38 M mutation (patient 30-3) was 7.6 microg/ml, an 8-fold increase compared with that of the wild type. The I37V mutation resulted in an IC(50) 3.2-fold greater than that of the wild type. Envs with double mutations (Q32R plus G36D and Q32H plus G36D) exhibited a level of resistance similar to that of G36D alone. These findings provide the first evidence for the rapid emergence of clinical resistance to a novel class of HIV-1 entry inhibitors and may be relevant to future treatment strategies involving these agents.

Crystal structure of the human class II MHC protein HLA-DR1 complexed with an influenza virus peptide

Abstract: An influenza virus peptide binds to HLA-DR1 in an extended conformation with a pronounced twist. Thirty-five per cent of the peptide surface is accessible to solvent and potentially available for interaction with the antigen receptor on T cells. Pockets in the peptide-binding site accommodate five of the thirteen side chains of the bound peptide, and explain the peptide specificity of HLA-DR1. Twelve hydrogen bonds between conserved HLA-DR1 residues and the main chain of the peptide provide a universal mode of peptide binding, distinct from the strategy used by class I histocompatibility proteins.