AFM studies of DNA structures on mica in the presence of alkaline earth metal ions

As counterions of DNA on mica, Mg(2+), Ca(2+), Sr(2+) and Ba(2+) were used for clarifying whether DNA molecules equilibrate or are trapped on mica surface. End to end distance and contour lengths were determined from statistical analysis of AFM data. It was revealed that DNA molecules can equilibrate on mica when Mg(2+), Ca(2+) and Sr(2+) are counterions. When Ba(2+) is present, significantly crossovered DNA molecules indicate that it is most difficult for DNA to equilibrate on mica and the trapping degree is different under different preparation conditions. In the presence of ethanol, using AFM we have also observed the dependence of B-A conformational transition on counterion identities. The four alkaline earth metal ions cause the B-A transition in different degrees, in which Sr(2+) induces the greatest structural transition.     

Interaction between the T4 helicase loading protein (gp59) and the DNA polymerase (gp43): unlocking of the gp59-gp43-DNA complex to initiate assembly of a fully functional replisome

Single-molecule fluorescence resonance energy transfer and functional assays have been used to study the initiation and regulation of the bacteriophage T4 DNA replication system. Previous work has demonstrated that a complex of the helicase loading protein (gp59) and the DNA polymerase (gp43) on forked DNA totally inhibits the polymerase and exonuclease activities of gp43 by a molecular locking mechanism (Xi, J., Zhuang, Z., Zhang, Z., Selzer, T., Spiering, M. M., Hammes, G. G., and Benkovic, S. J. (2005) Biochemistry 44, 2305-2318). We now show that this complex is unlocked by the addition of the helicase (gp41) with restoration of the DNA polymerase activity. Gp59 retains its ability to load the helicase while forming a gp59-gp43 complex at a DNA fork in the presence of the single-stranded DNA binding protein (gp32). Upon the addition of gp41 and MgATP, gp59 dissociates from the complex, and the DNA-bound gp41 is capable of recruiting the primase (gp61) to form a functional primosome and, subsequently, a fully active replisome. Functional assays of leading- and lagging-strand synthesis on an active replication fork show that the absence of gp59 has no effect on the coupling of leading- and lagging-strand synthesis or on the size of the Okazaki DNA fragments. We conclude that gp59 acts in a manner similar to the clamp loader to ensure proper assembly of the replisome and does not remain as a replisome component during active replication.     

Measurements of Cry1F binding and activity of luminal gut proteases in susceptible and Cry1F resistant Ostrinia nubilalis larvae (Lepidoptera: Crambidae)

The biochemical mechanism of resistance to the Bacillus thuringiensis Cry1F toxin was studied in a laboratory-selected strain of Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) showing more than 3000-fold resistance to Cry1F and limited cross resistance to other Cry toxins. Analyses of Cry1F binding to brush border membrane vesicles of midgut epithelia from susceptible and resistant larvae using ligand immunoblotting and Surface Plasmon Resonance (SPR) suggested that reduced binding of Cry1F to insect receptors was not associated with resistance. Additionally, no differences in activity of luminal gut proteases or altered proteolytic processing of the toxin were observed in the resistant strain. Considering these results along with previous evidence of relatively narrow spectrum of cross resistance and monogenic inheritance, the resistance mechanism in this Cry1F selected strain of O. nubilalis appears to be specific and may be distinct from previously identified resistance mechanisms reported in other Lepidoptera.     

Allotransplantation of adult spinal cord tissues after complete transected spinal cord injury: Long-term survival and functional recovery in canines

Science China Life Sciences - Spinal cord injury (SCI), especially complete transected SCI, leads to loss of cells and extracellular matrix and functional impairments. In a previous study, we...     

Dictyostelium phenylalanine hydroxylase is activated by its substrate phenylalanine

We have studied the regulatory function of Dictyostelium discoideum Ax2 phenylalanine hydroxylase (dicPAH) via characterization of domain structures. Including the full-length protein, partial proteins truncated in regulatory, tetramerization, or both, were prepared from Escherichia coli as his-tag proteins and examined for oligomeric status and catalytic parameters for phenylalanine. The proteins were also expressed extrachromosomally in the dicPAH knockout strain to examine their in vivo compatibility. The results suggest that phenylalanine activates dicPAH, which is functional in vivo as a tetramer, although cooperativity was not observed. In addition, the results of kinetic study suggest that the regulatory domain of dicPAH may play a role different from that of the domain in mammalian PAH.

Structured summary of protein interactions

dicPAH and dicPAHbind by molecular sieving (View Interaction: 1, 2, 3, 4)     

紫外线辐射对西伯利亚鲟精子活力和寿命的影响

研究了不同剂量紫外线辐射(254nm,UVC)对西伯利亚鲟精子活力和寿命的影响.结果表明:紫外线辐射对精子的活力、快速运动时间和寿命均具有显著性影响.其中,精子活力随辐射剂量的增加而呈先迅速下降,后迅速上升,再迅速下降的趋势;精子快速运动时间的变化趋势与活力相似;精子寿命随辐射剂量的增加呈缓慢下降的趋势.当辐射剂量达288mJ.cm-2时,精子无快速运动,当辐射剂量达324mJ.cm-2时,精子活力和寿命均降为0.根据Hertwig效应判断,辐射剂量216mJ.cm-2为西伯利亚鲟精子灭活的最适剂量.