A variation in the structure of the protein-coding region of the human p53 gene

An extensive analysis of genomic DNA preparations from a number of normal and malignant tissues revealed BglII site polymorphism of the human p53 gene. Approximately 10% of p53 gene alleles were found to contain an additional BglII site localized in a region of intron I. This allelic form of p53 gene was also responsible for p53 protein having altered electrophoretic mobility. Molecular cloning and sequencing of both the alleles of p53 gene revealed a base-pair change in codon 72 causing arginine → proline substitution in the allele with the additional BglII site. Both variants of the p53 gene may occur in homozygous state and are therefore functional.     

Effects of low-chloride solutions on action potentials of sheep cadiac purkinje fibers

The rapid repolarization during phase 1 of the action potential of sheep cardiac purkinje fibers has been attributed to a time- and voltage-dependent chloride current. In part, this conclusion was based on experiments that showed a substantial slowing of phase 1 when larger, presumably impermeant, anions were substituted for chloride in tyrode’s solution. We have re- examined the electrical effects of low-chloride solutions. We recorded action potentials of sheep cardiac purkinje fibers in normal tyrode’s solution and in low-chloride solutions made by substituting sodium propionate, acetylglycinate, methylsulfate, or methanesulfonate for the NaCl of Tyrode’s solution. Total calcium was adjusted to keep calcium ion activity of test solutions equal to that of control solutions. Propionate gave qualitatively variable results in preliminary experiments; it was not tested further. Low-chloride solutions made with the other anions gave much more consistent results: phase 1 and the notch that often occurs between phases 1 and 2 were usually unaffected, and the action potential duration usually increased. The only apparent change in the resting potential was a transient 3-6 mV depolarization when low-chloride solution was first admitted to the chamber, and a symmetrical transient hyperpolarization when chloride was returned to normal. If a time- and voltage-dependent chloride current exists in sheep cardiac purkinje fibers, our results suggest that it plays little role in generating phase 1 of the action potential.     

Anatomy of Bovine Mammillitis DNA I. Restriction Endonuclease Maps of Four Populations of Molecules That Differ in the Relative Orientation of Their Long and Short Components

In this paper, we report that the DNA of bovine mammillitis virus (BMV) consists of two covalently linked components that are 71.5 x 10(6) and 15.7 x 10(6) in molecular weight and designated L and S, respectively. We further report that the BMV DNA consists of four equimolar populations differing only in the orientation of the L and S components relative to each other. This conclusion is based on the following: (i) The sum molecular weight of fragments generated by digestion of BMV DNA with Hsu I, Hpa I, Bgl II, or Xba I significantly exceeds the established molecular weight of the intact DNA. (ii) In each digest, the fragments form three groups differing in molar concentration. In reference to the molar concentration of intact DNA, each enzyme digest contained a set of four fragments 0.25 M in concentration, a set of four fragments 0.5 M in concentration, and a variable size set, unique for each enzyme digest, 1.0 M in concentration. (iii) Experiments involving digestion of intact DNA by lambda exonuclease followed by restriction endonuclease digestion established that each of four 0.5 M fragments were positioned at the termini of the BMV DNA. (iv) Complete maps for the fragments generated by each enzyme established that the 0.25 M fragments arise by fusion of the sequences of the terminal fragments when these are juxtaposed as a consequence of the inversion of L and S components. The maps also established the dimensions of the L and S components. We conclude that the structure of BMV DNA is similar to that of HSV DNA previously shown to consist of two unequal size components that invert relative to each other.     

Plasminogen activator and collagenase production by cultured capillary endothelial cells

Cultured bovine capillary endothelial (BCE) cells produce low levels of collagenolytic activity and significant amounts of the serine protease plasminogen activator (PA). When grown in the presence of nanomolar quantities of the tumor promoter 12-O-tetradecanoyl phorbol-13-acetate (TPA), BCE cells produced 5-15 times more collagenolytic activity and 2-10 times more PA than untreated cells. The enhanced production of these enzymes was dependent on the dose of TPA used, with maximal response at 10(-7) to 10(-8) M. Phorbol didecanoate (PDD), an analog of TPA which is an active tumor promoter, also increased protease production. 4-O-methyl-TPA and 4α-PDD, two analogs of TPA which are inactive as tumor promoters, had no effect on protease production. Increased PA and collagenase activities were detected within 7.5 and 19 h, respectively, after the addition of TPA. The TPA-stimulated BCE cells synthesized a urokinase-type PA and a typical vertebrate collagenase. BCE cells were compared with bovine aortic endothelial (BAE) cells and bovine embryonic skin (BES) fibroblasts with respect to their production of protease in response to TPA. Under normal growth conditions, low levels of collagenolyic activity were detected in the culture fluids from BCE, BAE, and BES cells. BCE cells produced 5-13 times the basal levels of collagenolytic activity in response to TPA, whereas BAE cells and BES fibroblasts showed a minimal response to TPA. Both BCE and BAE cells exhibited relatively high basal levels of PA, the production of which was stimulated approximately threefold by the addition of TPA. The observation that BCE cells and not BAE cells produced high levels of both PA and collagenase activities in response to TPA demonstrates a significant difference between these two types of endothelial cells and suggests that the enhanced detectable activities are a property unique to bovine capillary and microvessel and endothelial cells.