DNA constraints on transcription activation in vitro.

Activators of eukaryotic transcription often function over a range of distances. It is commonly hypothesized that the intervening DNA between the transcription start site and the activator binding sites forms a loop in order to allow the activators to interact with the basal transcription apparatus, either directly or through mediators. If this hypothesis is correct, activation should be sensitive to the presence of intrinsic bends in the intervening DNA. Similarly, the precise helical phasing of such DNA bends and of the activator binding sites relative to the basal promoter should affect the degree of transcription activation. To explore these considerations, we designed transcription templates based on the adenovirus E4 promoter supplemented with upstream Gal4 activator binding sites. Surprisingly, we found that neither insertion of intrinsically curved DNA sequences between the activator binding sites and the basal promoter, nor alteration of the relative helical alignment of the activator binding sites and the basal promoter significantly affected in vitro transcription activation in HeLa cell nuclear extract. In all cases, the degree of transcription activation was a simple inverse function of the length of intervening DNA. Possible implications of these unexpected results are discussed.

A comparative analysis of pilin genes from pathogenic and nonpathogenic Neisseria species.

Pathogenic Neisseria species elaborate type IV pili, which are considered important for virulence. In this study, we examined pilin-encoding expression loci (pilE) in nonpathogenic Neisseria species. PCR based screening detected homology to a conserved N-terminal region of pilE in 12 of 15 Neisseria species, including all human commensal isolates. The three species failing to display homology were isolated from nonhuman sources. We have also characterized complete pilE loci from the human commensal species N. lactamica and N. cinerea. As anticipated, the predicted protein sequences from these species display features typical of all type IV pilins. In addition, these commensal pilins possess two highly conserved regions, SV2 and CYS2, which are shared among all neisserial pilins. However, a comparative analysis of pilE loci from pathogenic and nonpathogenic Neisseria species reveals two distinct structural groups, one composed of the pilin genes from N. lactamica, N. cinerea, and the class II pilin-producing subset of N. meningitidis isolates, the other of gonococcal and meningococcal class I pilin-encoding genes. Since both class I and class II pilin-producing meningococci can act as pathogens, structural relationships among neisserial pilin genes do not obviously reflect either species membership or ability to cause human disease.

Re-examining the concept of severity in traumatic brain injury.

This paper re-examines the theoretical concept of severe brain injury focusing on the duration of coma as a precise indicator of the clinical profile. A retrospective hospital chart study of 361 traumatic brain-injured patients was undertaken to determine the homogeneity of the subsample of the severely brain-injured (defined as 2 or more days of coma) with respect to the probability of four types of impairment: ataxia, contractures, paralysis and speech impairment. The current concept of severity assumes homogeneity among the 'severely brain-injured'. However, our results indicate significant differences in impairment within this population. The authors feel strongly that future studies must describe coma duration in finer gradations, and test for homogeneity within samples before inferences are made. Improvements in life-sustaining technologies have resulted in longer coma durations. The need to use coma days as an indicator of impairment rather than a broad category of severity is emphasized.