Deletion of the Penicillin-Binding Protein 6 Gene of Escherichia coli

A strain of Escherichia coli with a deletion of the penicillin-binding protein 6 gene (dacC) has been constructed. The properties of this strain establish that the complete lack of penicillin-binding protein 6 has no marked effect on the growth of E. coli.     

Isolation and mapping of the rRNA genes in the macronucleus of Oxytricha fallax

The DNA in the macronucleus of the protozoan Oxytricha, unlike like that of typical eukaryotes, exists as short, gene-sized molecules. Within the macronucleus the rRNA genes are contained in molecules 7,380 nucleotide pairs in length. This rDNA has been substanially purified by selective denaturation of non-ribosomal DNA followed by Sl nuclease digestion. Results from restriction nuclease digestion and rRNA:DNA hybridization show that the rDNA is a linear, non-palindromic molecule which contains one gene each for the 19s and 25s rRNAs. A total of less than 600 base pairs of DNA lies between the 19s and 25s genes or at the 3 end of the 25s gene. The non-coding portion of the ribosomal DNA is almost entirely limited to an approximately 1,400 base pair region at the 5 end of the molecule.     

Organization of the stomatogastric ganglion of the spiny lobster

Summary Three direct synaptic connections occur between neurons in the gastric and pyloric systems of the stomatogastric ganglion ofPanulirus interruptus. Two synapses are inhibitory, and one is electrical. This electrical synapse is both excitatory and inhibitory at different times. These synapses, and others within each system, let the two systems interact under some conditions. The synapses also form multisynaptic pathways which modulate the firing of many neurons in both systems. The consequences of these multisynaptic pathways are described and discussed.I thank Allen I. Selverston, Karen Sigvardt, Eve Marder, David Russell and Mary Chamberlin for criticizing a draft of this paper, Forrest Gompf and Doug Tissdale for technical support, and Nina Pollack and Betty Jorgensen for laboratory assistance. The research was supported by USPHS grant NS-12295 to BM and USPHS grant NS-09322 to Alien I. Selverston. BM was a USPHS NIH Postdoctoral Fellow in A.I. Selverston's laboratory during part of this research and is now a Research Fellow of the Alfred P. Sloan Foundation.     

Mutation in continuous cultures of Schizosaccharomyces Pombe. I. Dependence of the kinetics of mutation accumulation upon the growth-limiting nutrilite

The rate of spontaneous mutation to resistance to the 12,13-epoxytrichothecene trichodermin has been determined under different growth limiting conditions in continuous cultures of the microbial eukaryote Schizosaccharomyces pombe. In agreement with data obtained in bacterial systems by previous workers the kinetics observed for the accumulation of mutations is found to be dependent upon the nutrient used to limit the growth of the population. Under conditions of glucose-limitation mutation accumulation is directly proportional to the rate of cell division, while under histidine-limitation it is proportional to chronological time. Various possible explanations for these observations are discussed.     

Low serum testosterone concentrations in patients with carcinoma of the pancreas

The detection of high activities of two sex-steroid biosynthetic enzymes—aromatase and 5-alpha-reductase—in pancreatic carcinoma tissue suggested the possibility that these enzymes may influence the circulating concentrations of sex-steroid hormones. Mean serum testosterone concentrations in 22 men and women with exocrine carcinoma of the pancreas were significantly lower than those in 20 healthy controls and 27 patients with other known malignancies, who were of similar age and sex composition. Low serum testosterone concentrations may be due to uptake by and metabolism within the tumour; alternatively, patients with low androgen concentrations may be at greater risk of developing pancreatic carcinoma.