<p>The plant cyclin-dependent kinases (CDKs) are subjected to the regulation by the interactors/inhibitors of CDK (ICKs). Seven members of the ICK family are known in the plant <i>Arabidopsis thaliana</i>. It has been shown that the N-terminal region of ICK1 makes it unstable in plants, although the mechanism was unknown.</p> <p>In this thesis, to determine role of the N-terminal region in other ICKs, full length ICK2 to ICK7 were compared to truncated mutants lacking the N-terminal region. Results from yeast two-hybrid studies suggest that not all the N-terminal regions in different ICKs have a role similar to the N-terminal region of ICK1. Studies of a set of HA-tagged ICK1 deletion mutants in yeast mapped the critical sequence for ICK1 degradation to the N-terminal 21^st - 40^th amino acid residues. Overexpression of deletion mutants in Arabidopsis also showed that deletion of the 20-amino-acid region of ICK1 lead to a high level of HA-tagged mutant protein, supporting that this region plays a major role in ICK1 degradation <i>in vivo</i>.</p> <p>Treating yeast cells expressing HA-tagged ICK1 with the 26S proteasome inhibitor MG132 moderately increased the level of ICK1 protein, suggesting that 26S proteasome may be involved in the degradation of ICK1. To determine the possible involvement of the two E3 complexes, the Skp1-Cullin-F-box (SCF) complex and anaphase promoting complex/cyclosome (APC/C), a set of yeast mutants defective in either SCF complex or APC/C, were used to express ICK1, ICK1^ÎN20 (ICK1 lacking the N-terminal 20 amino acids) and ICK1^ÎN40. ICK1^ÎN40 showed a very high level of expression in SCF defective mutants, but not in APC/C defective mutants. However, ICK1 and ICK1^ÎN20 did not accumulate to a high level in either of the two types of mutants. These results suggest that two pathways are involved in the degradation of ICK1.</p> <p>Results from this study provide new understanding regarding the role of N-terminal region of ICK1 in conferring protein instability, and the differences among ICKs. They also raise new questions for future investigation on this family of plant cell cycle regulators.</p>

Besides collagen, elastin is the most common connective tissue structural protein in vertebrates and similar to collagen relatively resistant to non-specific degradation. Typical elastolytic proteases are the serine-dependent pancreatic and leukocyte elastases, the Zn-dependent matrix metalloproteinase 12, and several lysosomal cysteine proteases. Among the cysteine cathepsins, cathepsins S, K and V are highly potent elastases with cathepsin V displaying the highest activity among all known mammalian elastases. Despite a shared amino acid sequence identity of over 80% between cathepsins V and L and very similar subsite specificities, only cathepsin V has a potent elastase activity whereas cathepsin L lacks it. A series of chimera mutants containing various proportions of cathepsin V and cathepsin L were constructed in an attempt to define a specific region needed for elastin degradation. It was found that retaining the peptide sequence region from amino acids 89 to 119 of cathepsin V preserves the mutant’s elastolytic activity against elastin-Rhodamine conjugates whereas the region FTVVAPGK (amino acids 112-119) contributes approximately 60% of activity retention. Several additional mutant proteins involving mutual swapping of residues VDIPK (amino acids 113-117) of cathepsin L with residues TVVAPGK (amino acids 113-119) of cathepsin V, deletion of Glyl 18 from cathepsin V, and insertion of Gly between Prol 16 and Lysi 17 in cathepsin L were constructed and evaluated for their elastolytic activities. The results obtained with those mutant cathepsin proteins support the importance of the amino acid region spanning the residues from 112 to 119 in cathepsin V. Based on the 3-D structure of cathepsin V, this peptide region is located below subsite binding pocket S2 and forms a wall-like barrier which may act as an exosite for the productive binding of cross-linked elastin.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Commericially available BaTiO3 powder was die-pressed to discs, and sintered by a two-stage firing consisting of reducing in low oxygen partial pressures (pO2) and re-oxidizing in a higher pO2 to simulate the industrial process of manufacturing the multi-layer ceramic capacitors(MLCC). Both undoped and MgO-doped discs as well as commercial MLCC chips, provided by Ferro Electronic Material Systems, have been investigated for sintered microstructures using the scanning electron microscopy (SEM) and transmission electron microscopy (TEM), crystalline phases using the X-ray diffractometry (XRD), and dielectric properties using the frequency response analysis. A comparison between the microstructures is made in order to look for the microstructure origin of the macroscopic behaviour, e.g. dielectric properties.It is found that the crystalline phases have changed frompredominantly tetragonal to pseudo-cubic with MgO > 0.5 mol.%. Apart from grain growth being effectively suppressed in MgO-doped compositions, grains containing the characteristic ferroelectric domains in undoped samples have decreased significantly in number. The indication is that Mg2+ dissolving into the BaTiO3 lattice, substituting for the Ti4+ site reduces the c/a ratio. However, unlike what was reported before, no direct experimental evidence is found to support that grain growth inhibition is effected by Mg2+ segregation to grain boundaries.Dislocation loops are observed ubiquitously in all samples, although bothMgO doping and low pO2 have decisive effect on their density in sintered grains. In MLCC chips, the microstructure is characterised by core-shell grains representing the dissolution of solutes, and modulated grains representing the ordering of chemical defects, e.g. substitutional defects and oxygen vacancies forming defect clusters.Residual pores located intragranularly in the MLCC chips are also observed, and its origin discussed. The formation of such pores is attributed to vacancy condensation which is enhanced by the increased oxygen vacancies due to MgO doping, as an acceptor, and by low pO2 firing.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.