Integration into the bacterial

The small pieces of DNA known as plasmids, which replicate independently of the chromosomes, have been discussed briefly in Chapter 5. Plasmids share a number of properties with viruses, and both are important to the techniques of contemporary molecular biology and genetic engineering. Bacterial plasmids may be present as one or several copies for each chromosome. Episomes are plasmids that are able to become integrated into the bacterial chromosome. Some extrachromosomal elements are episomes in one host and plasmids in another. Bacterial... 

Episomes Plasmids that can imdergo integration into the bacterial chromosome. 

FIG. 14 Schematic illustration of an archaeal cell envelope structure (a) composed of the cytoplasmic membrane with associated and integral membrane proteins and an S-layer lattice, integrated into the cytoplasmic membrane, (b) Using this supramolecular construction principle, biomimetic membranes can be generated. The cytoplasmic membrane is replaced by a phospholipid or tetraether hpid monolayer, and bacterial S-layer proteins are crystallized to form a coherent lattice on the lipid film. Subsequently, integral model membrane proteins can be reconstituted in the composite S-layer-supported lipid membrane. (Modified from Ref. 124.)... 

Integration of the prophage into the bacterial ehromosome ensures that, on cell division, each daughter cell will acquire the set of viral genes. 

The pecM gene encodes a protein of 297 amino acids with a calculated molecular mass of 32 kDa. The predicted PecM protein displays the characteristics of an integral membrane protein since it is largely hydrophobic, with potential trans-membrane domains. SubceUular firactionation confirmed that PecM is anchored into the bacterial inner membrane whereas PecS is... 

Typically, functional porins are homotrimers, which assemble from monomers and then integrate into the outer membrane. The general porins, water-filled diffusion pores, allow the passage of hydrophilic molecules up to a size of approximately 600 Daltons. They do not show particular substrate specificity, but display some selectivity for either anions or cations, and some discrimination with respect to the size of the solutes. The first published crystal structure of a bacterial porin was that of R. capsulatus [48]. Together with the atomic structures of two proteins from E. coli, the phosphate limitation-induced anion-selective PhoE porin and the osmotically regulated cation-selective OmpF porin, a common scheme was found [49]. Each monomer consists of 16 (3-strands spanning the outer membrane and forming a barrel-like structure. 

Due to the carbon substrate requirement, photosynthetic bacterial systems are most suitable for integration into the second of a two-stage process, following a dark fermentation reaction. In this case the effluent from the first stage fermentation be comes the feedstock for the second stage photosynthetic process, as described above. 

However, it is already clear that the mechanisms responsible for membrane protein integration into the ER membrane and the inner bacterial membrane do place certain constraints on the allowable structures... 

---