SummaryNucleoid proteins are small, abundant, DNA-binding proteins that profoundly affect the local and global structure of the chromosome, and play a major role in gene regulation. Although several of these proteins have been shown to enhance assembly of transpososomes before initiating transposition, no systematic survey has been carried out examining the in vivo role(s) of these proteins in transposition. We have examined the requirement of the six most abundant nucleoid proteins in transposition for three different transposons, IS 903 , Tn 10 and Tn 552 . Most notably, H-NS was required for efficient transposition of all three elements in a papillation assay, suggesting a general role for H-NS in bacterial transposition. Further studies indicated that H-NS was exerting its effect on target capture. Targeting preferences for IS 903 into the Escherichia coli chromosome were dramatically altered in the absence of H-NS. In addition, the alterations observed in the IS 903 target profile emphasized the important role that H-NS plays in chromosome organization. A defect in target capture was also inferred for Tn 10 , as an excised transposon fragment, a precursor to target capture, accumulated in in vivo induction assays. Furthermore, a transposase mutant that is known to increase target DNA bending and to relax target specificity eliminated this block to target capture. Together, these results imply a role for H-NS in target capture, either by providing regions of DNA more accessible to transposition or by stabilizing transpososome binding to captured targets immediately before strand transfer.

The histone-like nucleoid structuring (H-NS) protein is a global transcriptional regulator that is known to regulate stress response pathways and virulence genes in bacteria. It has also been implicated in the regulation of bacterial transposition systems, including Tn10. We demonstrate here that H-NS promotes Tn10 transposition by binding directly to the transposition complex (or transpososome). We present evidence that, upon binding, H-NS induces the unfolding of the Tn10 transpososome and helps to maintain the transpososome in an unfolded state. This ensures that intermolecular (as opposed to self-destructive intramolecular) transposition events are favored. We present evidence that H-NS binding to the flanking donor DNA of the transpososome is the initiating event in the unfolding process. We propose that by recruiting H-NS as a modulator of transposition, Tn10 has evolved a means of sensing changes in host physiology, as the amount of H-NS in the cell, as well its activity, are responsive to changes in environmental conditions. Sensing of environmental changes through H-NS would allow transposition to occur when it is most opportune for both the transposon and the host.

Transepidermal water loss (TEWL) is a simple noninvasive measurement of inside-out skin barrier function. The goal of this research was to establish normal values for TEWL in early life using data gathered from the Cork BASELINE Birth Cohort Study. TEWL was recorded in a standardized fashion using a well-validated open-chamber system. A mean of three readings was recorded from 1,036 neonates (37-42 weeks gestational age) and 18 late preterm infants (34-37 weeks gestational age) within 96 hours of birth in an environmentally controlled room. Full-term neonatal TEWL measurements have a normal distribution (mean 7.06 ± 3.41 g of water/m(2) per hour) and mean preterm neonatal TEWL measurements were 7.76 ± 2.85 g of water/m(2) per hour. This is the largest evaluation to date of TEWL in a normal-term neonatal population. It therefore constitutes a reference dataset for this measurement using an open-chamber system.