Similarity of nucleotide sequences around the origin of DNA replication in mouse polyoma virus and simian virus 40

The nucleotide sequence around the origin of replication in DNA of mouse polyoma virus was determined by 32P labeling of the 3' terminus of the Hap II-5/Alu I-1 DNA fragment, with the use of DNA polymerase. The result coincided with our previous report on the 32P labeling, with the use of polynucleotide kinase, of the 5' terminus of the Hap II-5/Hha I-1 DNA fragment, which corresponds to the large part of the present fragment, Hap II-5/Alu I-1. A symmetrical (A+T)-rich region containing a five-A stretch (or a five-T stretch) was flanked by two small regions with a 2-fold rotational axis of symmetry. On comparison of the sequence near the replication origin of polyoma DNA with that in the corresponding region of simian virus 40 DNA, which was included in the EcoRI-G fragment sequenced by Weissman's group (Subramanian K.N., Dahr, R. & Weissman, S. M. (1977) J. Biol. Chem. 252, 355--367), a considerable similarity was detected. Several possible common sequences for important biological activities such as the starting of DNA replication and RNA synthesis were suggested.

Potassium activity and plasma membrane potentials in epithelial cells of toad bladder

Intracellular potassium activity (aki), mucosal and serosal membrane potential (mEm, sEm), short-circuit current (Isc), and transepithelial potential difference in the epithelium of the toad bladder were measured with a potassium-sensitive liquid ion exchanger and an ordinary microelectrode. Under basal conditions, aki was 41.2 +/- 0.5 mM, corresponding to 54.4 mM in free potassium concentration, so half or more of the intracellular potassium may be of bound form or sequestrated within subcellular organelles. The sEm cannot be explained by only the potassium equilibrium potential (Eeq), because the sEm was markedly lower than the Eeq and no relation was found between them. Ouabain and rotenone decreased the aki, but ethacrynic acid, which also inhibited the Isc and the membrane potentials, did not show any effect on aki. Vasopressin decreased aki with an elevation in mEm, whereas prostaglandin E1 increased the aki with elevation in the sEm. These characteristic changes may afford an insight into the mechanisms by which transcellular electrolyte transport occurs.

Decreased transforming ability of a temperature-sensitive mutant of human adenovirus type 12

A mutant of human adenovirus type 12, temperature-sensitive for virus replication an for the enhancement of thymidine incorporation in resting human embryonic kidney cells, is described. The mutant was also temperature-sensitive for transformation of rat cells. The results indicate that a viral gene required for the virus growth cycle is also required for transformation.

Effect of colchicine on the osmotic water flow across the toad urinary bladder

Osmotic water movement across the toad urinary bladder in response to both vasopressin and cyclic AMP was inhibited by 10(-5) to 10(-4) M colchicine on the serosal but not on the mucosal side. This inhibitory effect was found to be time- and dose-dependent. Colchicine alone did not change basal osmotic flow and a baseline of the short-circuit current (Isc) and also did not affect a vasopressin-induced rise of the Isc. The inhibitory effect was not prevented by the addition of pyruvate. The osmotic water movement produced by 360 mM Urea (mucosal), 360 mM mannitol (serosal) or 2 mug/ml amphotericin B (mucosal), was not affected by 10(-4) M colchicine. These results suggest that colchicine inhibits some biological process subsequent to the formation of cyclic AMP except a directional cytoplasmic streaming process where microtubules may be involved.

Rat cell line 3y1 and its virogenic polyoma- and sv40- transformed derivatives

Cell lines were established from cultures derived from Fischer rat embryos according to the transfer schedule described by Todaro and Green (1963) for mouse 3T3 cells where cell crowding and serum exhaustion were kept to a minimum. Cell growth rate did not decline greatly during the course of successive 3-day transfers. Like 3T3 cells the rat cell lines possess very low saturation desities under standard culture conditions. A clonal cell line with a relatively high plating efficiency as obtained from one of the cell lines, 3YL. In these cloned cultures, virus growth was not detectable upon infection with SV40, while a small amount of virus was produced upon infection with polyoma virus. Morphological transformation of the cloned 3Y1 cells by SV40 and polyoma virus could be assayed with single-hit kinetics and with effieiencies comparable to those of the previously available transformation systems for each virus. Independent cell lines transformed by SV40 were consistently virus-free and all the lines tested produced SV40 upon fusion with permissive monkey cells. Most of the independent transfromed cell lines isolated after polyoma infection appeared to be virus-free, although the cultures of some lines produced a small amount of polyoma virus spontaneously after a prolonged cultivation. Most of the virus-free polyoma-transformed lines produced virus upon fusion with permissive mouse cells.

Initiation and maintenance of cell transformation by simian virus 40: a viral genetic property

The transforming ability in 10% serum medium of the temperature-sensitive mutants of simian virus 40 in the complementation group III (ts640 type mutants) was greatly reduced when the infected rat 3Y1 cells were incubated at the restrictive temperature of 40 degrees or incubated first at 40 degrees for 3 days and then shifted to the permissive temperature of 33 degrees. Transformation did occur efficiently after incubation at 33 degrees or after an initial incubation at 33 degrees for 5 days followed by a shift to 40 degrees. When growth properties of 3Y1 cells transformed at 33 degrees by the group III mutants were examined at 40 degrees, several aspects of the transformed state were rendered temperature-sensitive. These aspects were the ability of cells to grow in low serum (1.5%) medium and to make colonies, in 10% serum medium, on monolayers of untransformed 3Y1 cells and in soft agar. It is concluded that a simian virus 40 gene (cistron III) controls the initiation, as well as at least some aspects of the maintenance, of transformation and that the initiation reaction is a more heat-labile event than the maintenance reaction(s) under the experimental conditions.