The outer membrane of E. coil contains two major protein, OmpF and OmpC, which allow the passive diffusion of small hydrophilic molecules across the membrane. Expression of the genes coding for these proteins is affected in a reciprocal manner by the medium osmolarity. This osmoregulation is controlled at the transcriptional level by two protein factors, EnvZ and OmpR. The OmpR protein is the positive regulator specific for the ompF and ompC genes. The EnvZ protein was assumed to sense an environmental osmotic signal and then somehow modulate the OmpR function. The results of recent studies clearly imply that the phosphotransfer reactions between the EnvZ and OmpR proteins play roles in the signal transduction and the consequent osmoregulatory exression of the ompF and ompC genes in vivo. It was suspected that protein phosphorylation is commonly involved in the regulation of gene activation and signal transduction observed for a variety of prokaryotic two-component regulatory systems.
Anumber of genes in E. coli, including phoA, pstS, phoE, and ugpB, are related to transport and assimilation of phosphate and are under the same physiological and genetic controL. They constitute a single pho regulon and are regulated by multiple regulatory genes that constitute a cascade regulatory network. In this system, the modulator protein PhoR undergoes autophosphorylation in the presence of ATP and acts as a protein kinase for the activator protein PhoB. Phosphorylation of PhoB enhances its binding activity to the pho box and activates transcription from the pho promoters.
The inner and outer dynein arms in eukaryotic flagella are key protein assemblies responsible for force production. Although the two types of arm have been believed to have similar properties, studies on newly isolated Chlamydomonas mutants lacking either of them indicate that they differ strikingly in structure and function; for example, flagella lacking the entire outer arms are motile, whereas those lacking the entire inner arm are nonmotile. These studies suggest that the inner and outer arms play different roles in flagellar motility, and raise a problem of how they cooperate to produce efficient flagellar beating.
Plasmids are present in distinct copy numbers in exponentially growing cells. It means the frequency of replication initiation of plasmid DNA is defined in these cells. A large group of plasmids like pSC101 contains directly repeating, 18 to 21 base pairs sequences in the replication origin. The Rep protein encoded by the plasmid genome binds to the repeated sequences to function as an initiator of DNA replication. The protein has an additional function of a repressor to regulate its own synthesis by binding to the promotor region of its structure gene. Regulation of replication initiation by the Rep protein is discussed.
The DNA replication origin region of Escherichia coli chromosome, oriC, in which GATC sequences are located abundantly, was investigated by means of differential scanning calorimetry. Adenine methylation of GATC sequences by Dam enzyme makes melting of the oriC region very easy, suggesting that this property has a significant role in initiation of oriC DNA replication. Other origin regions were also described.
Scientists are talking with beer about current topics on membrane protein rotation and protein-protein interactions related to (1) electron trnasport in mitochondrial respiratory chain, (2) drug-induction and lipid peroxidation in liver microsomal drug oxidation system and, (3) adrenocortial steroid hormone synthesis system.