Among the biological phenomena that fall within the emerging field of “quantum biology” is the suggestion that magnetically sensitive chemical reactions are responsible for the magnetic compass of migratory birds. It has been proposed that transient radical pairs are formed by photo-induced electron transfer reactions in cryptochrome proteins and that their coherent spin dynamics are influenced by the geomagnetic field leading to changes in the quantum yield of the signaling state of the protein. Despite a variety of supporting evidence, it is still not clear whether cryptochromes have the properties required to respond to magnetic interactions orders of magnitude weaker than the thermal energy, k B T . Here we demonstrate that the kinetics and quantum yields of photo-induced flavin—tryptophan radical pairs in cryptochrome are indeed magnetically sensitive. The mechanistic origin of the magnetic field effect is clarified, its dependence on the strength of the magnetic field measured, and the rates of relevant spin-dependent, spin-independent, and spin-decoherence processes determined. We argue that cryptochrome is fit for purpose as a chemical magnetoreceptor.

Cholesterol molecules were put into a computer-modeled hydrated bilayer of dimyristoyl phosphatidyl choline molecules, and molecular dynamics simulations were run to characterize the effect of this important molecule on membrane structure and dynamics. The effect was judged by observing differences in order parameters, tilt angles, and the fraction of gauche bonds along the hydrocarbon chains between lipids adjacent to cholesterol molecules and comparing them with those further away. It was observed that cholesterol causes an increase in the fraction of trans dihedrals and motional ordering of chains close to the rigid steroid ring system with a decrease in the kink population. The hydrogen-bonding interactions between cholesterol and lipid molecules were determined from radial distribution calculations and showed the cholesterol hydroxyl groups either solvated by water, or forming hydrogen bond contacts with the oxygens of lipid carbonyl and phosphate groups. The dynamics and conformation of the cholesterol molecules were investigated and it was seen that they had a smaller tilt with respect to the bilayer normal than the lipid chains and furthermore that the hydrocarbon tail of the cholesterol was conformationally flexible.

A 1.2-kilobase-pair BamHl fragment from a cell envelope-cell division gene cluster of Escherichia coli containing ddl and part offtsQ was cloned and sequenced, and the sequence was interpreted with the aid of genetic complementation and promoter fusion data for the region. Both ddl and ftsQ were transcribed in the same direction (clockwise on the genetic map). ddl was shown to be capable of independent expression from a promoter of its own, and a promoter was identified within the ddl structural gene. The structural gene of ddl consisted of 918 nucleotides, encoding a 306-residue polypeptide of molecular weight 32,840; the synthesis of a protein of this molecular weight was shown to be directed from the 1.2-kilobase-pair BamHI fragment in minicells. Analysis of the DNA sequence further showed that the termination codon of ddl is separated from the initiation codon offtsQ by one base, which suggests that these two genes may be translationally coupled when transcription is initiated upstream of ddl. This represents a second instance of potential translational coupling within this gene cluster and also indicates that the ddl and ftsQ transcriptional units must overlap (as has been reported earlier for ftsQ and ftsA and for ftsA and ftsZ).The 2-min region of the Escherichia coli K-12 genetic map (1) contains a large cluster of genes which are involved in cell envelope growth and division. Moving clockwise around the map, the genes for murein biosynthesis, mraA, mraB, ftsI, murE, murF, murG, murC, and ddl (1, 41), precede a cluster of essential cell division genes, ftsQ, ftsA, and ftsZ (3, 21), which in turn are followed by the cell permeability-cell separation gene envA (28). The functions of only some of the gene proucts from this region are known. The murein genes specify enzymes which are required for the biosynthesis of the cell wall (17, 18), and a mutation in the ddl gene is associated with an impaired D-alanine:D-alanine ligase activity (19). A mutation in envA has been shown to cause a reduced level of N-acetylmuramyl-L-alanine amidase activity (42), and an ftsZ(Ts) mutant (PAT84) exhibits a low activity of D-alanine-carboxypeptidase at the restrictive temperature (25). Lutkenhaus (20) has shown that sulB is an allele of ftsZ and that the ftsZ protein is a target for an SOS-inducible inhibitor of cell division; this inhibitor is the product of the sulA (sfiA) gene (14). Jones and Holland (16) have used transpositional mutagenesis to map the position of a dominant sfiB allele (sfiB114). This allele renders partial diploids of an sfiB+ E. coli host resistant to the SOSmediated division inhibition response. They found that sfiBJ14 was located withinfftsZ.

When cells carrying the plasmids RP1, pDS4101 (a ColK derivative) or pDS1109 (a ColE1 derivative) were maintained in chemostat culture in the absence of antibiotic selection, plasmid-free segregants were not detected after 120 generations of nutrient-limited growth. By contrast, plasmid-free segregants of pMB9- and pBR322-containing cells arose after approximately 30 generations, irrespective of the host genetic background. However, even though pDS1109 was maintained its copy-number fell five-fold during 80 generations of limited growth. It is suggested that loss of pBR322 occurs following a similar copy-number decrease which results in defective segregation of the plasmid to daughter host cells. This defective segregation was not complemented in trans by either RP1 or pDS4101.

1 The mitogen-activated protein kinases (MAPKs) consist of the p42/p44 MAPKs and the stressactivated protein kinases, c-Jun N-terminal kinase (JNK) and p38 MAPK. In this study we have examined the e ect of histamine H 1 receptor activation on MAPK pathway activation in the smooth muscle cell line DDT 1 MF-2. 2 Histamine stimulated time and concentration-dependent increases in p42/p44 MAPK activation in DDT 1 MF-2 cells. Responses to histamine were inhibited by the histamine H 1 receptor antagonist mepyramine (K D 3.5 nM) and following pre-treatment with pertussis toxin (PTX; 57% inhibition). 3 Histamine-induced increases in p42/p44 MAPK activation were blocked by inhibitors of MAPK kinase 1 (PD 98059), tyrosine kinase (genistein and tyrphostin A47), phosphatidylinositol 3-kinase (wortmannin and LY 294002) and protein kinase C (Ro 31-8220; 10 mM; 41% inhibition). Inhibitors of Src tyrosine kinase (PP2) and the epidermal growth factor tyrosine kinase (AG1478) were without e ect. Removal of extracellular Ca 2+ , chelation of intracellular Ca 2+ with BAPTA and inhibition of focal adhesion assembly (cytochalasin D) had no signi®cant e ect on histamine-induced p42/p44 MAPK activation. 4 Histamine stimulated time and concentration-dependent increases in p38 MAPK activation in DDT 1 MF-2 cells but had no e ect on JNK activation. Histamine-induced p38 MAPK activation was inhibited by pertussis toxin (74% inhibition) and the p38 MAPK inhibitor SB 203580 (95% inhibition). 5 In summary, we have shown the histamine H 1 receptor activates p42/p44 MAPK and p38 MAPK signalling pathways in DDT 1 MF-2 smooth muscle cells. Interestingly, signalling to both pathways appears to involve histamine H 1 receptor coupling to G i /G o -proteins.