Protein conformation in bacterial spinae

The far uv circular dichroism (CD) and infrared spectra of bacterial spinae are reported. Estimates of the protein secondary structure were obtained by three-component curve-fitting methods supplemented by rank and factor analysis of CD data matrices. Native spinae were shown to contain approximately 88% antiparallel β-sheet, 7% α-helix, and 5% unordered structure based on estimates using poly(L -lysine). Basis CD spectra derived from globular proteins were shown to give unreliable estimates.     

The attachment of bacterial spinae.

Spinae are attached to protease-sensitive structural proteins in the external surface of the outer membrane. Agents and (or) treatments affecting ionic, hydrophobic, or hydorgen bonds are ineffective in releasing spinae from bacteria. As judged by thin-sectioning and freeze-fracturing techniques, the outer membrane is not modified at the attachment site to a detectable extent, and the other surface layers are not involved. The attachment of spinae is thus differentiated from that of flagella.     

Remembering silence.

Polycomb response elements (PREs) are regulatory switch elements that can direct the genes that they control to be either active or silenced. Once decided, this on or off state is maintained through subsequent cell divisions. We do not know how the switching works, or how it is copied to newly replicated chromosomes. Experiments that switch a silenced PRE to an active state have provided insights into both questions. A PRE switched experimentally can remember its previously silenced state and return to it after several cell divisions. In the most recent study of this phenomen on, the data show that several distinct variables affect the ability of PREs to "remember" and restore their previous state. The authors' interpretation of these results is discussed here.     

The signs of silence

How does auditory cortex respond to silence? In this issue of Neuron, show that activity in macaque auditory cortex is highly structured even in the absence of sensory stimuli. These data reveal a close link between spontaneous neural activity and the functional organization of auditory cortex.     

Spreading silence with Sid

RNA interference (RNAi) has been shown to spread from cell to cell in plants and in Caenorhabditis elegans, but it does not spread in other organisms, such as Drosophila. A recent report demonstrates that a membrane channel, encoded by the gene sid-1, is responsible for the spreading of RNAi between cells.     

Complexity beneath the silence

Polycomb group (PcG)-mediated silencing by proteins that are conserved across plants and animals is a key feature of eukaryotic gene regulation. Investigation of PcG-mediated gene silencing has revealed a surprising degree of complexity in the molecular mechanisms that recruit the protein complexes, repress expression, and maintain the epigenetic silent state of target genes. This review summarizes our current understanding of the mechanism of PcG-mediated gene silencing in animals and higher plants.