[Motor competence and quality of life in elderly active persons]. / Motorische Handlungskompetenz und Lebensqualität älterer aktiver Menschen.

Physical activity is a vital pre-condition for healthy aging and well-being. While the association between objective and subjective health in old age has extensively been investigated, the relationship between objective motor competence-the capability of mastering motor demands in everyday life adequately by using motor resources optimally-and subjective health-related quality of life has not been studied yet. In an interdisciplinary study, 168 active seniors (36 men) at the mean age of 67 (range: 59-89) underwent a test battery assessing motor resources and two objective domains of everyday life motor competence-"Perceiving and Reacting" and "Mastering Complex Situations". Subsequently, participants rated their mental, physical, social, functional health and life satisfaction by questionnaire. Motor competence domains were age-dependent; the strongest decrease was found for "Mastering Complex Situations". Only "Mastering Complex Situations" was predicted by motor resources: competent seniors in this domain were faster in motor activity, simple reactions, body movements following acoustic and optic signals, and showed a stronger handcraft and a higher mobility. Overall, health-related quality of life was contingent upon motor competence: physical and functional health and-to a lesser extent-mental health and life satisfaction showed a systematic but moderate relationship to both motor competence domains. The results emphasize the significance of age-compatible and everyday life-adjusted physical activity for the well-being of elderly persons. Even active elderly persons show deficits in motor competence and should be trained, taking into account individual resources and flaws.

Endocytotic uptake and retrograde transport of a virally encoded killer toxin in yeast.

We demonstrate that a virally encoded yeast 'killer' toxin is entering its eukaryotic target cell by endocytosis, subsequently travelling the yeast secretory pathway in reverse to exhibit its lethal effect. The K28 killer toxin is a secreted alpha/beta heterodimer that kills sensitive yeasts in a receptor-mediated fashion by blocking DNA synthesis in the nucleus. In vivo processing of the toxin precursor results in a protein whose beta-C-terminus carries the endoplasmic reticulum (ER) retention signal HDEL, which, as we show here, is essential for retrograde toxin transport. Yeast end3/4 mutants as well as cells lacking the HDEL receptor (Deltaerd2) or mutants defective in Golgi-to-ER protein recycling (erd1) are toxin resistant because the toxin can no longer enter and/or retrograde pass the cell. Site-directed mutagenesis further indicated that the toxin's beta-HDEL motif ensures retrograde transport, although in a toxin-secreting yeast the beta-C-terminus is initially masked by an R residue (beta-HDELR) until Kex1p cleavage uncovers the toxin's targeting signal in a late Golgi compartment. Prevention of Kex1p processing results in high-level secretion of a biologically inactive protein incapable of re-entering the secretory pathway. Finally, we present evidence that ER-to-cytosol toxin export is mediated by the Sec61p translocon and requires functional copies of the lumenal ER chaperones Kar2p and Cne1p.

The mouse mammary tumour virus promoter positioned on a tetramer of histones H3 and H4 binds nuclear factor 1 and OTF1.

Modulation of eukaryotic gene expression is influenced by the organization of regulatory DNA-elements in chromatin. The mouse mammary tumor virus (MMTV) promoter exhibits regularly positioned nucleosomes that reduce the accessibility of the binding sites for sequence-specific transcription factors, in particular nuclear factor (NF1). Hormonal induction of the MMTV promoter is accompanied by remodeling of the nucleosomal structure, but the biochemical nature of these structural changes is unknown. Using recombinant histones, we have now assembled the MMTV promoter in particles containing either an octamer of the histones H3, H4, H2A and H2B or a tetramer of histones H3 and H4, and have compared the two particles in terms of structure, positioning, and exclusion of transcription factors. Using site-directed hydroxy radicals to map histone locations, two main nucleosome positions are found with dyads at position -107 and at -127. The same two main positions are found for particles containing only the H3/H4 tetramer, showing that the absence of H2A/H2B dimers does not alter positioning. The rotational orientation of the DNA double helix in both types of particles is essentially identical. However, the ends of the nucleosomal DNA as well as its central region are more accessible to cleavage reagents in the tetramer particle than in the octamer particle. In agreement with these structural features, the transcription factors NF1 and OTF1 were able to bind to their cognate sites on the tetramer particle, while they could not gain access to the same sites on the surface of the octamer particle. The DNase I digestion pattern of octamers treated with partially purified SWI/SNF complex from HeLa cells in the presence of ATP is indistinguishable from that of tetramer particles, suggesting that the SWI/SNF complex promotes ATP-dependent remodeling of the octamer particle but not of tetramer particles. These results are compatible with a hormone-induced removal of histone H2A/H2B during MMTV induction.

Transcription factor access to chromatin.

The question of how sequence-specific transcription factors access their cognate sites in nucleosomally organized DNA is discussed on the basis of genomic footprinting data and chromatin reconstitution experiments. A classification of factors into two categories is proposed: (i) initiator factors which are able to bind their target sequences within regular nucleosomes and initiate events leading to chromatin remodelling and transactivation; (ii) effector factors which are unable to bind regular nucleosomes and depend on initiator factors or on a pre-set nucleosomal structure for accessing their target sequences in chromatin. Studies with the MMTV promoter suggest that the extent and number of protein-DNA contacts determine whether a factor belongs to one or the other category. Initiator factors have only a few DNA contacts clustered on one side of the double helix, whereas effector factors have extensive contacts distributed throughout the whole circumference of the DNA helix. Thus, the nature of DNA recognition confers to sequence-specific factors their specific place in the sequential hierarchy of gene regulatory events.

Binding of NF1 to the MMTV promoter in nucleosomes: influence of rotational phasing, translational positioning and histone H1.

To analyse the role of rotational orientation and translational positioning of nucleosomal DNA on transcription factor binding we have generated a series of mutant MMTV promoters containing insertions of various lengths between the hormone-responsive region and the binding site for NF1. These various MMTV promoter fragments were assembled in mononucleosomes and used for structural studies and binding experiments. We show that the insertions change the rotational phase and translational positioning of the NF1 site as predicted if the sequences upstream of the insertion site were the main determinants of nucleosome phasing. In band shift experiments with recombinant NF1 we cannot detect binding of the protein to NF1 sites included within the limits of a nucleosome, independent of their rotational orientation. Moving the NF1 site closer to the nucleosome border also did not permit NF1 binding. This behaviour probably reflects the way NF1 binds DNA, namely it almost completely surrounds the circumference of the double helix establishing a large number of contacts with the bases and the backbone. In contrast to the wild-type and short insertion mutants, NF1 bound readily to nucleosomes containing 30 or 50 bp insertions which placed the NF1 site at the nucleosome edge or within linker DNA. NF1 binding to the linker DNA was unaffected by incorporation of histone H1 into the nucleosome particle. These findings are discussed in relation to chromatin remodelling initiated by steroid hormones during induction of the MMTV promoter.