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We have analyzed the contributions of specific domains of DnaB helicase to its quaternary structure and multienzyme activities. Highly purified tryptic fragments containing various domains of DnaB helicase were prepared. Fragment I lacks 14 amino acid (aa) residues from the N-terminal of DnaB helicase. Fragments II and III are 33-kDa C-terminal and 12-kDa N-terminal polypeptides, respectively, of fragment I. The single-stranded DNA-dependent ATPase and DNA helicase activities of DnaB helicase and its fragments were examined in detail. The ATPase activities of native DnaB helicase and fragment I were comparable; however, the ATPase activity of fragment II was somewhat diminished. Unlike the ATPase activity, the DNA helicase activity was totally abolished in fragment II and was not complemented by the addition of equimolar fragment III. Consequently, the N-terminal 17-kDa domain appeared to have an indispensable role in the DNA helicase action, but not in other enzymatic activities. Fragment I had a hexameric structure similar to that observed with DnaB helicase in both size exclusion HPLC (SE-HPLC) and chemical cross-linking studies. SE-HPLC analysis indicated that fragment II had an apparent hexameric form. However, a detailed chemical cross-linking analysis showed that it formed stable dimers but the formation of a stable hexamer was severely impaired. Thus, the N-terminal domain appeared to have a strong influence on the hexamer formation.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of starch carbamoylethylation upon the adhesion capability of starch to pure cotton, all polyester, and polyester/cotton blend fiber substrates were investigated. The carbamoylethyl starch was prepared by the reaction of starch with acrylamide in an aqueous dispersion. The capability was evaluated in terms of the maximum strength and work-to-break of a roving impregnated with the starch pastes. The mechanical behaviors of the adhesive layers were estimated through a method by casting starch films and then by measuring their behaviors under controlled condition. It was found that the carbamoylethylation is an effective means for enhancing the adhesion of starch to fibers. No matter what type of the fibers is used, the adhesion capability obviously enhances compared with those of unmodified starch, even if the degree of substitution is at a very low level. The capacity increases steadily as the modification extent increases. Moreover, the experimental results are also discussed and analyzed especially through the failure type, internal stress, stress concentration, and mechanical behaviors of the adhesive layers among fibers.

To strengthen national competitiveness and sustainability, the high-tech industry has been developed as the center of gravity of industrial development in each country, covering the development of new products and the expansion to new customers and markets. Although both aspects are indispensable to high-tech firms’ growth momentum and competitive advantages, it is difficult to develop them at the same time. In recent years, scholars have been paying an increasing amount of attention to the significance of organizational ambidexterity in different management fields. Importantly, transformed high-tech firms are obliged to manage the tensions and conflicts that arise from the exploration of new knowledge and the exploitation of existing knowledge to find an appropriate balance between the two to yield synergistic effects. In this study, an original method was used to measure differences in the degree of ambidexterity. The method establishes a multiplicative term of exploration and exploitation to represent the degree of effect of ambidexterity. The higher the exploration and exploitation are, the higher the degree of ambidexterity will be. This study takes as its objects electronics manufacturing firms in Taiwan that engage in the development of new high-tech products. We issued a total of 1000 questionnaires to electronics manufacturing firms in Taiwan and received 228 valid ones. The results indicate that exploitation has a positive effect on performance, and there is an inverse U-shaped correlation between exploration/exploitation and performance. Ambidexterity and its interaction with the market orientation were found to have a positive influence on organizational performance. We also investigated the extent to which an organization places emphasis on resources and the influence of resource allocation on organizational performance. We suggest that the co-existence of exploration and exploitation is important to organizational performance. Accordingly, developing the two capabilities at the same time conforms to the concept of ambidexterity.

The modulation of enzymatic activities of Escherichia coli DnaB helicase by homologous and heterologous single-stranded DNA-binding proteins (SSBs) and its DNA substrates were analyzed. Although DnaB helicase can unwind a variety of DNA substrates possessing different fork-like structures, the rate of DNA unwinding was significantly diminished with substrates lacking a 3' fork. A 5 nt fork appeared to be adequate to attain the maximum rate of DNA unwinding. Efficient helicase action of DnaB requires the participation of SSBs. Studies involving heterologous SSBs demonstrated that they can stimulate the helicase activity of DnaB protein under certain conditions. However, this stimulation occurs in a manner distinctly different from that observed with cognate E.coli SSB. The E.coli SSB was found to stimulate the helicase activity over a wide range of SSB concentrations and was unique in its strong inhibition of single-stranded DNA-dependent ATPase activity when uncoupled from the DNA helicase activity. In the presence of a helicase substrate, the ATPase activity of DnaB helicase remained uninhibited. Thus, E.coli SSB appears to coordinate and couple the ATPase activity to the DNA helicase activity by suppressing unproductive ATP hydrolysis by DnaB helicase.