Construction of a human cytochrome c gene and its functional expression in Saccharomyces cerevisiae

The nucleotide sequences of a partial cDNA and three pseudogenes of human cytochrome c were determined. The complete nucleotide sequences which encode human cytochrome c were constructed on the basis of one of the pseudogenes by in vitro mutagenesis. The constructed human cytochrome c was functionally expressed in Saccharomyces cerevisiae. The recombinant human cytochrome c was purified and characterized.     

Interaction between the Msh2 and Msh6 Nucleotide-binding Sites in the Saccharomyces cerevisiae Msh2-Msh6 Complex

Indirect evidence has suggested that the Msh2-Msh6 mispair-binding complex undergoes conformational changes upon binding of ATP and mispairs, resulting in the formation of Msh2-Msh6 sliding clamps and licensing the formation of Msh2-Msh6-Mlh1-Pms1 ternary complexes. Here, we have studied eight mutant Msh2-Msh6 complexes with defective responses to nucleotide binding and/or mispair binding and used them to study the conformational changes required for sliding clamp formation and ternary complex assembly. ATP binding to the Msh6 nucleotide-binding site results in a conformational change that allows binding of ATP to the Msh2 nucleotide-binding site, although ATP binding to the two nucleotide-binding sites appears to be uncoupled in some mutant complexes. The formation of Msh2-Msh6-Mlh1-Pms1 ternary complexes requires ATP binding to only the Msh6 nucleotide-binding site, whereas the formation of Msh2-Msh6 sliding clamps requires ATP binding to both the Msh2 and Msh6 nucleotide-binding sites. In addition, the properties of the different mutant complexes suggest that distinct conformational states mediated by communication between the Msh2 and Msh6 nucleotide-binding sites are required for the formation of ternary complexes and sliding clamps.     

Retention of bone cell viability in mouse calvarial explants after cryopreservation

Newborn mouse calvaria, cyropreserved at -196 degrees C in serum-free medium containing dimethyl-sulfoxide, were compared to unpreserved explants for bone cell viability by [3H]thymidine uptake. Other explants were studied using autoradiography to compare the histological appearance of the cryopreserved and control unpreserved explant sites of cellular localization of [3H]thymidine. After short-term cryopreservation, calvarial bone cells, including less differentiated osteoprogenitor cells, survived as indicated by their incorporation of the DNA precursor. With culture continuing for up to 24 hr after thawing and in the continuous presence of [3H]thymidine, additional labeled thymidine was incorporated, indicating that the proliferative ability of explant cells persists after cryopreservation. Cryopreserved bone explants did not, however, incorporate the same amount of labeled thymidine as did controls at each time point studied. These events, as measured quantitatively and observed by autoradiography of the tissue, indicate that newborn calvarial bone cell proliferation in vitro continues after cryopreservation. The large surface:mass ratio of the tissue and its proportionate volume of calcified matrix apparently permits it to behave as an isolated cell population with regard to the diffusion of the cryoprotectant and thermal conductivity, thus permitting the retention of explant viability.     

DIFFERENTIAL INCORPORATION OF [3H]LYSINE INTO VISUAL CORTEX PROTEIN FRACTIONS DURING FIRST EXPOSURE TO LIGHT

—A resolution of the enhancement of protein synthesis in the visual cortex of rats during first exposure to light (Richardson and Rose , 1972) was achieved by polyacrylamide gel electrophoresis using a double-labelling technique. Differential incorporation of lysine was established between exposed and control animals in two fractions of the soluble proteins and seven fractions of the insoluble proteins. This suggests that exposure to a new experience of this type involves a specific effect on protein synthesis, rather than a general stimulation across all fractions.