Crystallographic studies of the chicken gizzard G-actin X DNase I complex at 5A resolution

The structure of the chicken gizzard G-actin X DNase I complex has been determined at 5 A resolution by an X-ray diffraction method. Protein phases were computed by the multiple isomorphous replacement method using four heavy atom derivatives. The mean figure of merit was 0.65. Dimensions of the three molecular species, the complex, G-actin and DNase I, were determined based on the "cypress wood" models derived from the electron density map. The natures of the heavy atom binding sites are discussed in relation to the distinction between the two component molecules. The pattern of successive contacts between actin molecules observed in the present crystal seems unrelated to that found in F-actin.     

Biosynthesis of the common precursor to vasopressin and neurophysin in vitro in transplantable human oat cell carcinoma of the lung with ectopic vasopressin production

Transplantable human oat cell carcinoma cells of the lung with ectopic vasopressin production were incubated with labeled amino acids and immunoreactive neurophysins in cell extracts were analyzed by isoelectric focusing. When the cells were incubated with L-(35S)-cysteine for 20 h, one major peak (isoelectric point; pI=5.3) and several minor peaks (pI=6.1, 5.7, 5.1, 4.9 and 4.7) of labeled proteins were observed. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the relative molecular mass (Mr) of the pI 5.7 protein was estimated to be 20,000 and that of the pI 6.1 species to be 19,000, while the remainder had a Mr of approximately 10,000. The result of the pulse-labeling experiment has clearly shown that the pI 5.7 and 6.1 proteins, which have affinity for concanavalin A, are biosynthetic precursors for the smaller form of neurophysin with a pI 5.3. When subjected to limited proteolysis with trypsin, the pI 5.7 protein generated a Mr 10,000 protein and a smaller peptide. The Mr 10,000 protein thus produced was identified as neurophysin on the basis of its pH-dependent affinity for vasopressin and the migration pattern on isoelectric focusing. The smaller peptide coeluted with synthetic arginine vasopressin and bound to neurophysin suggesting that it possesses a cysteine-tyrosyl sequence at its N-terminus. Similarly, the pI 6.1 protein liberated neurophysin and vasopressin-like peptide after incubation with trypsin. These results suggests that the glycosylated protein with a pI of 5.7 and a Mr of 20,000 is the common precursor to vasopressin and neurophysin in human oat cell carcinoma of the lung with ectopic vasopressin production. The pI 6.1 protein may be an intermediate in the conversion of the precursor to vasopressin and neurophysin.     

Immunological specificity and biological action of biliary glucagon-like substance in the rabbit

A glucagon-like substance named biliary IRG2000 whose molecular weight is approximately 2,000 was isolated by gel filtration from rabbit bile. This substance showed a strong crossreactivity as equivalent to 25.7 +/- 5.1 ng/ml of porcine glucagon in RIA with antiserum 30K specificity. Biliary IRG2000 brought about a significant increase and delayed the response of blood glucose level in coexistence with porcine glucagon, though it has no appreciable effect on the glucose level when administered singly to the mouse intraperitoneally. The response with the coexistence of these materials was far greater than when porcine glucagon was given alone. In Mortimore's type rat liver perfusion, a significant rise in glucose concentration in effluent was also observed when a mixture of biliary IRG2000 and porcine glucagon was perfused. The rate of 125I-glucagon degradation was found delayed in the presence of biliary IRG2000 when examined in the rat. Thus the increase and delayed response of glucose level in coexistence of porcine glucagon with biliary IRG2000 may be explained by a suppressive effect of glucagon degradation due to biliary IRG2000.     

Long-term cultivation of amphibian melanophores. In vitro ageing and spontaneous transformation to a continuous cell line

Pure melanophore populations isolated from the tail skin of the tadpole, Rana catesbeiana, were mass cultured for a period of 2-3 years. All cell lines of amphibian melanophores studied exhibited growth crisis (in vitro ageing) followed by spontaneous transformation to a continuous cell line, as shown by changes in growth characteristics in mass culture and in clone culture, by the appearance of the cells, and by measurements of cell volumes. Even after becoming a continuous cell line, amphibian melanophores continued to have a diploid chromosome number (2n = 26) in three of four cell lines examined. The chromosome mode in one cell line, however, changed to thirty. Measurement of melanin dispersion after the addition of alpha-melanocyte-stimulating hormone suggested that the mechanism for melanin dispersion in melanophores changed during in vitro ageing.     

Phase Shift in the Potassium Uptake Rhythm of the Duckweed Lemna gibba G3 Caused by an Azide Pulse

A 6-hour application (6-hour pulse) of 1 millimolar azide significantly changed the phase of the potassium uptake rhythm of Lemna gibba G3. The phase response curve obtained was type 0 and very similar to that caused by a 6-hour pulse of low temperature (5°C) or darkness. The magnitude of the phase shift and the type of the phase response curve depended on the concentration of azide. However, 6-hour pulses of 3 millimolar cyanide or 10 micromolar (3-(3,4-dichlorophenyl)-1,1-dimethylurea) failed to shift the phase of the rhythm, while these pulses lowered the rate of carbon dioxide uptake or release. Azide, even at 3 micromolar, selectively reduced the amplitude of the rhythm without inhibiting the mean level of potassium uptake.     

Mapping of the human gene for epidermal growth factor receptor (EGFR) on the p13 leads to q22 region of chromosome 7

We previously reported that the structural gene for epidermal growth factor receptor (EGFR) can be mapped to the p22 leads to qter region of human chromosome 7 (Shimizu et al., 1979, 1980). In the present study, we produced two series of human-mouse cell hybrids by fusing mouse A9 cells that are deficient in EGFR with the human diploid fibroblast lines GM1356, 46,XX,t(1;7)(p34;p13), and GM2068, 46,XX,t(6;7)(q27;q22), both of which possess EGF receptors. Expression of EGF binding ability in the former series of cell hybrids was correlated with the retention of the human translocation chromosome containing the 7p13 leads to qter region, and in the latter series of cell hybrid it was correlated with the retention of the human translocation chromosome containing the 7pter leads to q22 region. Therefore, the EGFR gene can be localized in the p13 leads to q22 region of chromosome 7.