Structure-function studies of the bacteriophage T4 DNA polymerase. Isolation of a novel suppressor mutant

We describe here our first attempt in using suppressor mutations to study structure-function relationships of the bacteriophage T4 DNA polymerase. One intragenic suppressor mutation, J5(43) degrees, was isolated that suppresses the temperature sensitivity but not the mutator activity of tsM19, a DNA polymerase mutant. Thus, the substituted amino acid induced by the tsM19 lesion decreases DNA polymerase fidelity, even if the temperature sensitivity has been corrected by a second amino acid substitution in the DNA polymerase polypeptide. The isolation, mapping and characterization of the J5(43) degrees mutation as well as the purification and characterization of the tsM19-J5(43) degrees mutant DNA polymerase are presented. The suppressor isolation procedure has general applicability for the selection of suppressor mutations of other T4 DNA polymerase mutator mutants.     

MV-mimicking micelles loaded with PEG-serine-ACP nanoparticles to achieve biomimetic intra/extra fibrillar mineralization of collagen in vitro

Since their discovery, matrix vesicles (MVs) containing minerals have received considerable attention for their role in the mineralization of bone, dentin and calcified cartilage. Additionally, MVs' association with collagen fibrils, which serve as the scaffold for calcification in the organic matrix, has been repeatedly highlighted. The primary purpose of the present study was to establish a MVs–mimicking model (PEG-S-ACP/micelle) in vitro for studying the exact mechanism of MVs-mediated extra/intra fibrillar mineralization of collagen in vivo. In this study, high-concentration serine was used to stabilize the amorphous calcium phosphate (S-ACP), which was subsequently mixed with polyethylene glycol (PEG) to form PEG-S-ACP nanoparticles. The nanoparticles were loaded in the polysorbate 80 micelle through a micelle self-assembly process in an aqueous environment. This MVs–mimicking model is referred to as the PEG-S-ACP/micelle model. By adjusting the pH and surface tension of the PEG-S-ACP/micelle, two forms of minerals (crystalline mineral nodules and ACP nanoparticles) were released to achieve the extrafibrillar and intrafibrillar mineralization, respectively. This in vitro mineralization process reproduced the mineral nodules mediating in vivo extrafibrillar mineralization and provided key insights into a possible mechanism of biomineralization by which in vivo intrafibrillar mineralization could be induced by ACP nanoparticles released from MVs. Also, the PEG-S-ACP/micelle model provides a promising methodology to prepare mineralized collagen scaffolds for repairing bone defects in bone tissue engineering.     

An inexpensive photosynthetic irradiance sensor for ecological field studies

The design and characteristics of inexpensive and simply constructed equal-energy response photosynthetic irradiance sensors is described for use particularly where several cells are required in comparative ecological studies either above or below water. The dimensions of the sensors can be changed proportionally to suit different applications or components. The response of the sensor to irradiance at varying angles corresponds very closely to that required by the cosine law. The sensor is comparatively insensitive to other environmental variables in field use and gave a stable output; the long term drift was proportional to electrical output but in continuous use, drift is regular and could reach -0.08 year^-1 of the total. The spectral range and cosine response is discussed in comparison to other more expensive (x 5–10) commercially available, sensors and to local standards.     

Light induced transpiration in a chlorophyll deficient mutant of Hordeum vulgare

A chlorophyll deficient mutant of Hordeum vulgare L. was investigated with respect to its transpiration response to light pulses. Broad band blue light. 380–500 nm, caused a significant transpiration response, while broad band red light did not. The transpiration response to changes in the ambient CO₂-concentration was the same in the chlorophyll deficient mutant as in green plants. The absence of a transpiration response to red light in the mutant was therefore not the result of a defective CO₂-response. It is concluded that the specific blue light response is not mediated via photosynthetic CO₂-fixation. The nature of the blue light response is discussed.     

Chlorophyll b accumulation and grana formation in low intensities of red light

Abstract When dark grown leaves of wheat (Triticum aesivum L.) were given a brief irradiation, there was an immediate onset of chlorophyll (Chl) b synthesis in the dark. This synthesis led to a rather slow accumulation of Chl b, which ceased when the Chl b/Chl a ratio had reached a value of about 0.1. The Chl b synthesis occurred also when the seedlings were treated with the herbicide SAN 9789. Leaves grown under different intensities of red light accumulated Chl b and Chl a, resulting in a ratio Chl b/Chl a which depended on the light intensity. If the light intensity was low, Chl a accumulated to a level about ten times the level of PChlide of the dark grown leaves. This occurred without any increase in the Chl b/Chl a ratio. There was no difference between SAN 9789-treated seedlings and water controls in this respect. Above a certain threshold of irradiance, the Chl b/Chl a ratio in the control leaves increased rapidly with the irradiation intensity. The increase in Chl b/Chl a ratio coincided with formation of grana in the plastids. This increase was not found and grana formation was completely absent in the seedlings treated with SAN 9789. The possibility of two different stages in the Chl b synthesis is discussed.