Calf thymus Hsc70 protein protects and reactivates prokaryotic and eukaryotic enzymes.

The heat-shock 70 protein (Hsp70) chaperone family is very conserved and its prokaryotic homologue, the DnaK protein, is assumed to form one of the cellular systems for the prevention and restoration of heat-induced protein denaturation. By using anti-DnaK antibodies we purified the DnaK homologue heat-shock cognate protein (Hsc70) from calf thymus to apparent homogeneity. This protein was classified as an eukaryotic Hsc70, since (i) monoclonal antibodies against eukaryotic Hsc70 recognized it, (ii) its amino-terminal sequence showed strong homology to Hsp70s from eukaryotes and, (iii) it had an intrinsic weak ATPase activity that was stimulated by various peptide substrates. We show that this calf thymus Hsc70 protein protected calf thymus DNA polymerases alpha and epsilon as well as Escherichia coli DNA polymerase III and RNA polymerase from heat inactivation and could reactivate these heat-inactivated enzymes in an ATP-hydrolysis dependent manner, likely leading to the dissociation of aggregates formed during heat inactivation. In contrast to this, DnaK protein was exclusively able to protect and to reactivate the enzymes from E.coli but not from eukaryotic cells. Finally, the addition of calf thymus DnaJ co-chaperone homologue reduced the amount of Hsc70 required for reactivation at least 10-fold

Nucleo-cytoplasmic transport of proteins and RNA in plants

Merkle T. Nucleo-cytoplasmic transport of proteins and RNA in plants. Plant Cell Reports. 2011;30(2):153-176.Transport of macromolecules between the nucleus and the cytoplasm is an essential necessity in eukaryotic cells, since the nuclear envelope separates transcription from translation. In the past few years, an increasing number of components of the plant nuclear transport machinery have been characterised. This progress, although far from being completed, confirmed that the general characteristics of nuclear transport are conserved between plants and other organisms. However, plant-specific components were also identified. Interestingly, several mutants in genes encoding components of the plant nuclear transport machinery were investigated, revealing differential sensitivity of plant-specific pathways to impaired nuclear transport. These findings attracted attention towards plant-specific cargoes that are transported over the nuclear envelope, unravelling connections between nuclear transport and components of signalling and developmental pathways. The current state of research in plants is summarised in comparison to yeast and vertebrate systems, and special emphasis is given to plant nuclear transport mutants

Elements of transcriptional machinery are compatible among plants and mammals

Wolf A, Akrap N, Marg B, et al. Elements of transcriptional machinery are compatible among plants and mammals. PLoS ONE. 2013;8(1): e53737.In the present work, the objective has been to analyse the compatibility of plant and human transcriptional machinery. The experiments revealed that nuclear import and export are conserved among plants and mammals. Further it has been shown that transactivation of a human promoter occurs by human transcription factor NF-κB in plant cells, demonstrating that the transcriptional machinery is highly conserved in both kingdoms. Functionality was also seen for regulatory elements of NF-κB such as its inhibitor IκB isoform α that negatively regulated the transactivation activity of the p50/RelA heterodimer by interaction with NF-κB in plant cells. Nuclear export of RelA could be demonstrated by FRAP-measurements so that RelA shows nucleo-cytoplasmic shuttling as reported for RelA in mammalian cells. The data reveals the high level of compatibility of human transcriptional elements with the plant transcriptional machinery. Thus, Arabidopsis thaliana mesophyll protoplasts might provide a new heterologous expression system for the investigation of the human NF-κB signaling pathways. The system successfully enabled the controlled manipulation of NF-κB activity. We suggest the plant protoplast system as a tool for reconstitution and analyses of mammalian pathways and for direct observation of responses to e.g. pharmaceuticals. The major advantage of the system is the absence of interference with endogenous factors that affect and crosstalk with the pathway

Agrobacterium tumefaciens VirC2 enhances T-DNA transfer and virulence through its C-terminal ribbon–helix–helix DNA-binding fold

Agrobacterium tumefaciens VirC2 stimulates processing of single-stranded T-DNA that is translocated into plants to induce tumor formation, but how VirC2 functions is unclear. Here, we report the 1.7-Å X-ray crystal structure of its trypsin-resistant C-terminal domain, VirC282–202, which reveals a form of the ribbon-helix-helix (RHH) DNA-binding fold contained within a single polypeptide chain. DNA-binding assays and mutagenesis indicate that VirC2 uses this RHH fold to bind double-stranded DNA but not single-stranded DNA. Mutations that severely affect VirC2 DNA binding are highly deleterious for both T-DNA transfer into yeast and the virulence of A. tumefaciens in different plants including Nicotiana glauca and Kalanchoe daigremontiana. These data suggest that VirC2 enhances T-DNA transfer and virulence through DNA binding with its RHH fold. The RHH fold of VirC2 is the first crystal structure representing a group of predicted RHH proteins that facilitate endonucleolytic processing of DNA for horizontal gene transfer

A proteomic analysis of oligo(dT)-bound mRNP containing oxidative stress-induced Arabidopsis thaliana RNA-binding proteins ATGRP7 and ATGRP8

Schmidt F, Marnef A, Cheung M-K, et al. A proteomic analysis of oligo(dT)-bound mRNP containing oxidative stress-induced Arabidopsis thaliana RNA-binding proteins ATGRP7 and ATGRP8. Molecular Biology Reports. 2010;37(2):839-845.Plants are highly adapted to respond to a range of environmental stresses commonly by altering their gene expression and metabolism as a result of cell signalling which may be mediated by reactive oxygen species. The glycine-rich RNA-binding proteins AT GRP7 and AT GRP8 were rapidly upregulated in response to peroxide-induced oxidative stress and were amongst the most abundant RNA binding proteins isolated by oligo(dT) chromatography. The oligo(dT)-bound mRNP complexes were analysed proteomically, and were seen to contain potential isoforms of the AT GRP proteins; other proteins that contain an RNA Recognition Motif (RRM); and chloroplast RNA binding proteins. These findings suggest that AT GRP proteins have an evolutionarily conserved function in the regulation of gene expression at the posttranscriptional level in response to environmental stress