Sable and umbrous mice

Summary An umbrous gene in the house mouse is described which is transmitted in crosses as a simple dominant. The same gene is capable of engendering a sable phenotype with yellow and an umbrous-agouti with white-bellied agouti. It assorts independently of the agouti locus, with which it was specifically tested, and probably of sex. The manifestation of the gene is briefly contrasted with other known cases of umbrous heredity.     

Three Years' Experience with Implanted Pacemakers

At the University Hospital, Saskatoon, over the last three years, pacemakers have been inserted in 40 patients with complete or incomplete heart block. Fourteen of the patients were females and 26 were males. The average age was 65 years; 12 were over 80 years of age, and the youngest patient was 8 years of age. In none was the heart block due to operation. Thirty-three patients are still alive and well. There have been seven deaths three early and four late. One patient died because of a “runaway” pacemaker, and two as a result of infection persisting around the pacemaker. Twenty-nine Medtronic pacemakers were used and 14 Atricor pacemakers; currently we favour the latter instrument.     

In vitro differentiation of rabbit blastocyst cells

Summary Six- and seven-day post-coitus (p.c.) rabbit embryos have been cultured in an attempt to establish a trophectodermal cell line. Results indicate that cells with epithelial characteristics (i.e. positive staining for cytokeratin) will survive in culture until Passage 3. At that time a fibroblastlike cell becomes predominant. In addition, we have found that the presence of the inner cell mass is required for embryo explants often results in the development of cells that spontaneously contract. These cells stain positively for myosin, which indicates that they may be precardiac cells. Maximum diastolic potential was −59±1.2 mV and the threshold potential was −53±2.3 mV. Spontaneously contracting cells did not respond to atropine, acetylcholine, epinephrine, isoproterenol, or propranolol. Action potential seems to be a result of an inward calcium current, because the beating rate is decreased in a dose-related manner with the calcium channel blocker verapamil, whereas the voltage-sensitive sodium channel blocker tetrodotoxin was without effect. This work was supported by grants HD21302, HD07069, DK31091, and HL37320 from the National Institutes of Health, Bethesda, MD, with additional support from a University of Alabama at Birmingham Cardviovascular Research and Training Center Award.     

srRNA evolution and phylogenetic relationships of the genus Naegleria (Protista: Rhizopoda)

A rapid RNA sequencing technique was used to partially sequence the small-subunit ribosomal RNA (srRNA) of four species of the amoeboid genus Naegleria. The extent of nucleotide sequence divergence between the two most divergent species was roughly similar to that found between mammals and frogs. However, the pattern of variation among the Naegleria species was quite different from that found for those species of tetrapods characterized to date. A phylogenetic analysis of the consensus Naegleria sequence showed that Naegleria was not monophyletic with either Acanthamoeba castellanii or Dictyostelium discoideum, two other amoebas for which sequences were available. It was shown that the semiconserved regions of the srRNA molecule evolve in a clocklike fashion and that the clock is time dependent rather than generation dependent.     

Purification and properties of RhaR, the positive regulator of the L-rhamnose operons of Escherichia coli

The product of the rhaR gene, which regulates the level of mRNA produced from the four L-rhamnose-inducible promoters of the rhamnose operon, has been hypersynthesized and purified by a two-column procedure. The purified protein is a 33 kDa DNA-binding protein that binds to an inverted repeat structure located within the psr promoter, the promoter for the rhaS and rhaR genes. The equilibrium binding constants and kinetic constants have been determined under a variety of solution conditions. The protein binds with high affinity and its binding is sensitive to salt concentration and the presence of L-rhamnose. The nucleotides and phosphate residues contacted by RhaR were identified by chemical interference assays. All of the contacts are made to one face of the DNA and the symmetrical pattern matches the inverted repeat sequence proposed for the binding site. An unusual property of the binding site is that the two half-sites of the inverted repeat are separated from one another by 17 base-pairs of uncontacted DNA. Significant binding is retained if the 17 base-pairs are extended by insertions of integral turns of DNA, but not by half-integral turns. The complex of RhaR-DNA appears to be sharply bent, approximately 160 degrees.     

Localization of α-amylase isozymes within the endomembrane system of barley aleurone

Summary The localization of -amylase (EC 3.2.1.1) in barley (Hordeum vulgare L. cv Himalaya) aleurone protoplasts was studied using electron microscope immunocytochemistry. Antibodies were raised against total barley -amylase, i.e., -amylase containing both highisoelectric point (high-pI) and low-pI isoforms, as well as against purified high- and low-pI isoforms. All antibodies localized -amylase to the endoplasmic reticulum (ER) and Golgi apparatus (GApp) of the aleurone cell, and various controls showed that the labeling was specific for -amylase. Labeling of protein bodies and spherosomes, which are the most abundant organelles in this cell, was very low. There was no evidence that -amylase isoforms were differentially distributed within different compartments of the endomembrane system. Rather, both high- and low-pI isoforms showed the same pattern of distribution in ER and in the cis, medial, and transregions of the GApp. We conclude that in the Himalaya cultivar of barley, all isoforms of -amylase are transported to the plasma membrane via the GApp.Abbreviations ER endoplasmic reticulum - GA₃ gibberellic acid - GApp Golgi apparatus - PBS phosphate buffered saline - PCR partially coated reticulum - PM plasma membrane - TBS Tris buffered saline - TGN trans-Golgi network