Circular deoxyribonucleic acid from Shigella dysenteriae Y6R

Circular deoxyribonucleic acid was isolated from Shigella dysenteriae Y6R and was found to consist of six species having molecular weights of 10(6), 1.3 x 10(6), 2.6 x 10(6), 3.8 x 10(6), 20 x 10(6), and 24 x 10(6) daltons. These size classes were partially resolved by sucrose density gradient centrifugation. The minicircles (10(6) and 1.3 x 10(6)) were found to have a buoyant density in CsCl of 1.710 g/ml. The 3.8 x 10(6) dalton class had a density of 1.707 g/ml. The two largest species had a density of 1.702 g/ml. Two other strains, S. sonnei II and S. dysenteriae 60, also contained circular deoxyribonucleic acid.     

Chest wall motion during epidural anesthesia in dogs

To determine the relative contribution of rib cage and abdominal muscles to expiratory muscle activity during quiet breathing, we used lumbar epidural anesthesia in six pentobarbital sodium-anesthetized dogs lying supine to paralyze the abdominal muscles while leaving rib cage muscle motor function substantially intact. A high-speed X-ray scanner (Dynamic Spatial Reconstructor) provided three-dimensional images of the thorax. The contribution of expiratory muscle activity to tidal breathing was assessed by a comparison of chest wall configuration during relaxed apnea with that at end expiration. We found that expiratory muscle activity was responsible for approximately half of the changes in thoracic volume during inspiration. Paralysis of the abdominal muscles had little effect on the pattern of breathing, including the contribution of expiratory muscle activity to tidal breathing, in most dogs. We conclude that, although there is consistent phasic expiratory electrical activity in both the rib cage and the abdominal muscles of pentobarbital-anesthetized dogs lying supine, the muscles of the rib cage are mechanically the most important expiratory muscles during quiet breathing.     

Isolation and characterization of a mutation that alters the substrate specificity of the Escherichia coli glucose permease.

We isolated 10 mannitol-positive mutants from a mannitol-negative Escherichia coli strain. These mutations mapped within ptsG, encoding the glucose permease (EIIGlc), and resulted in a G-320-to-V substitution that allows EIIGlc to transport mannitol. Gly-320 lies within a putative transmembrane helix of EIIGlc that may be involved in substrate recognition.     

Cyclin D1 transgene impedes lymphocyte maturation and collaborates in lymphomagenesis with the myc gene.

Cyclin D1 is the regulatory subunit of certain protein kinases thought to advance the G1 phase of the cell cycle. Deregulated cyclin D1 expression has been implicated in several human neoplasms, most consistently in centrocytic B lymphoma, where the cyclin D1 gene usually has been translocated to an immunoglobulin locus. To determine directly whether constitutive cyclin D1 expression is lymphomagenic, transgenic mice were generated having the cyclin D1 gene linked to an immunoglobulin enhancer. Despite abundant transgene expression, their lymphocytes were normal in cell cycle activity, size and mitogen responsiveness, but young transgenic animals contained fewer mature B- and T-cells. Although spontaneous tumours were infrequent, lymphomagenesis was much more rapid in mice that co-expressed the cyclin D1 transgene and a myc transgene than in mice expressing either transgene alone. Moreover, the spontaneous lymphomas of myc transgenic animals often ectopically expressed the endogenous cyclin D1 gene. These findings indicate that this G1 cyclin can modulate differentiation and collaborate with myc-like genes in oncogenesis.