Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Prokaryotes have a complex cell envelope which has several important functions, including providing a barrier that protects the cytoplasm from the environment. Along with its associated proteinaceous structures, it also ensures cell stability, facilitates motility, mediates adherence to biotic and abiotic surfaces, and facilitates communication with the extracellular environment. Viruses have evolved to take advantage of cell envelope constituents to gain access to the cellular interior as well as for egress from the cell. While many aspects of the biosynthesis and structure of the cell envelope are similar across domains, archaeal cell envelopes have several unique characteristics including, among others, an isoprenoid lipid bilayer, a non-murein-based cell wall, and a unique motility structure, important features that give archaeal cell envelopes characteristics that are significantly different from those of bacterial cell envelopes. Recent analyses have revealed that the cell envelopes of distantly related archaea also display an immense diversity of characteristics. For instance, while many archaea have an S-layer, the subunits of S-layers of various archaeal species, as well as their posttranslational modifications, vary significantly. Moreover, like gram-negative bacteria, recent studies have shown that some archaeal species also have an outer membrane. In this collection of articles, we include contributions that focus on research that has expanded our understanding of the mechanisms underlying the biogenesis and functions of archaeal cell envelopes and their constituent surface structures.

Archaebacteria. --- Microbiology. --- pili --- membrane --- Biofilms --- hami --- Archaea --- S-layer --- Cytochromes --- Surface structures --- Flagella --- archaella

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

DNA replication, a central event for cell proliferation, is the basis of biological inheritance. Complete and accurate DNA replication is integral to the maintenance of the genetic integrity of organisms. In all three domains of life, DNA replication begins at replication origins. In bacteria, replication typically initiates from a single replication origin (oriC), which contains several DnaA boxes and the AT-rich DNA unwinding element (DUE). In eukaryotic genomes, replication initiates from significantly more replication origins, activated simultaneously at a specific time. For eukaryotic organisms, replication origins are best characterized in the unicellular eukaryote budding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe. The budding yeast origins contain an essential sequence element called the ARS (autonomously replicating sequence), while the fission yeast origins consist of AT-rich sequences. Within the archaeal domain, the multiple replication origins have been identified by a predict-and-verify approach in the hyperthermophilic archaeon Sulfolobus. The basic structure of replication origins is conserved among archaea, typically including an AT-rich unwinding region flanked by several short repetitive DNA sequences, known as origin recognition boxes (ORBs). It appears that archaea have a simplified version of the eukaryotic replication apparatus, which has led to considerable interest in the archaeal machinery as a model of that in eukaryotes. The research on replication origins is important not only in providing insights into the structure and function of the replication origins but also in understanding the regulatory mechanisms of the initiation step in DNA replication. Therefore, intensive studies have been carried out in the last two decades. The pioneer work to identify bacterial oriCs in silico is the GC-skew analysis. Later, a method of cumulative GC skew without sliding windows was proposed to give better resolution. Meanwhile, an oligomer-skew method was also proposed to predict oriC regions in bacterial genomes. As a unique representation of a DNA sequence, the Z-curve method has been proved to be an accurate and effective approach to predict bacterial and archaeal replication origins. Budding yeast origins have been predicted by Oriscan using similarity to the characterized ones, while the fission yeast origins have been identified initially from AT content calculation. In comparison with the in silico analysis, the experimental methods are time-consuming and labor-intensive, but convincing and reliable. To identify microbial replication origins in vivo or in vitro, a number of experimental methods have been used including construction of replicative oriC plasmids, microarray-based or high-throughput sequencing-based marker frequency analysis, two-dimensional gel electrophoresis analysis and replication initiation point mapping (RIP mapping). The recent genome-wide approaches to identify and characterize replication origin locations have boosted the number of mapped yeast replication origins. In addition, the availability of increasing complete microbial genomes and emerging approaches has created challenges and opportunities for identification of their replication origins in silico, as well as in vivo and in vitro.

orisome --- Replication Origin --- Cell-cycle --- Archaea --- origin recognition complex (ORC) --- Bacteria --- DNA Replication --- Replication regulation --- yeast --- Regulatory proteins