Surface layers of Eubacterium yurii subsp. yurii and their possible role in test-tube brush formation and iron acquisition.

Eubacterium yurii subsp. yurii is an anaerobic, gram-positive rod. On isolation E. yurii forms cellular arrangements resembling test-tube brushes (TTB). Although TTB decreased in size and number on repeated laboratory subculture in enriched media, media poor in available iron enhanced formation of these. Plasmids were not demonstrated, even after chloramphenicol enhancement. To characterise the nature and possible physiological roles of the structures of the TTB, they were examined by transmission electronmicroscopy (TEM) with thin-section, negative-staining, shadow-casting, freeze-etching and freeze-fracturing techniques, and by scanning electronmicroscopy (SEM). Previous studies by phase-contrast microscopy revealed an amorphous core, the size of which varied in direct proportion to the number of associated bacterial cells. Thin sections of the TTB showed a gram-positive cell wall with additional surface layers. Negative staining, shadow casting and freeze etching revealed a surface layer comprising subunits in tetragonal array (P4 symmetry). Shadow casting showed also that the outermost layer of the cells was composed of fibrillar structures closely associated with but distinct from, the tetragonal layer. The fibrils extended from the cell surface in clumps or strands. The presence of these fibrils was confirmed by the freeze-fracture technique and SEM. Chemical analysis of the core material of the TTB showed it to be low in carbohydrate (0.06%) and protein (0.2%). Energy-dispersive X-ray spectrometry showed that the core was composed mostly of iron.(ABSTRACT TRUNCATED AT 250 WORDS)     

Some issues in the assessment of clinical practice: a review of the literature

? This paper focuses on some issues in the assessment of clinical practice of particular interest to the author. ? The assessment of students of nursing in clinical practice is acknowledged as a long-standing and difficult problem. ? There is little consensus as to what is meant by the term competence when applied to clinical nursing practice, making the assessment of clinical practice a mainly subjective process. ? The English National Board (1989) has distinguished the term mentor as meaning counsellor and guide, nevertheless the roles of mentor and assessor are frequently confused. ? It is suggested that nurses are equally accountable for the accurate assessment of student nurses' clinical skills as they are for their own practice. ? The validity and reliability of tools used to assess clinical practice are difficult to establish, making objective assessment complex at best, and impossible at worst. ? The assessment of the reflective process has been suggested as one way out of the dilemma, but the ability to think and to write does not necessarily translate into competent clinical practice.     

Biological characterization of Drosophila Rapgap1, a GTPase activating protein for Rap1

The activity of Ras family proteins is modulated in vivo by the function of GTPase activating proteins, which increase their intrinsic rate of GTP hydrolysis. We have isolated cDNAs encoding a GAP for the Drosophila Rap1 GTPase. Drosophila Rapgap1 encodes an 850-amino acid protein with a central region that displays substantial sequence similarity to human RapGAP. This domain, when expressed in Escherichia coli, potently stimulates Rap1 GTPase activity in vitro. Unlike Rap1, which is ubiquitously expressed, Rapgap1 expression is highly restricted. Rapgap1 is expressed at high levels in the developing photoreceptor cells and in the optic lobe. Rapgap1 mRNA is also localized in the pole plasm in an oskar-dependent manner. Although mutations that completely abolish Rapgap1 function display no obvious phenotypic abnormalities, overexpression of Rapgap1 induces a rough eye phenotype that is exacerbated by reducing Rap1 gene dosage. Thus, Rapgap1 can function as a negative regulator of Rap1-mediated signaling in vivo.