Genetic regulation of a constitutive operon in E. coli B-r

Genetics and regulation of D-xylose utilization in Salmonella typhimurium LT2

Twenty-one Xyl- mutants of Salmonella typhimurium were selected: all had lost one or more of the activities for D-xylose isomerase, C-xylulokinase, or D-xylose transport. The mutants were classified into five functional groups: xylR, pleiotropic negative (12 mutants); xylA, D-xylose isomerase defective (3 mutants); xylB, D-xylulokinase defective (2 mutants); xylT, D-xylose transport defective (1 mutant); and 3 mutants with defective D-xylose isomerase and D-xylulokinase. Some nonsense mutations were identified among the xylR mutants. Two F'xyl plasmids were isolated by selection for early transfer of xyl+ by an Hfr which transfers xyl as a terminal gene; a plasmid with a mutation in the xyl genes, F'xylR1, was also isolated. Complementation tests using F'xyl plasmids indicate that expression of the xylA, xylB, and xylT genes is under the positive control of the xylR regulatory gene. Conjugation crosses and P22-mediated transduction data indicate that all the xyl mutations tested are in a cluster of genes at 78 units on the linkage map, and that the gene order is xylT--xylR--xylB--xylA--glyS--mtlA,D.

Genetic regulation of the constitutive D-ribose operon in Escherichia coli B/r

Merodiploid complementation analysis of the constitutive synthesis of the D-ribokinase and the D-ribose permease in Escherichia coli B/r has shown that the constitutive D-ribose operon is genetically controlled by a transdominant regulatory gene closely linked to the D-ribokinase and D-ribose permease structural genes. The regulatory mechanism for this operon shows no requirement for operator-repressor interaction, rather a truly positive control mechanism and thus suggests an extension of the operon model in its application to constitutive enzyme regulation in bacteria.

The site of synthesis and functions of acute phase plasma proteins: close relationship with the reticulo-endothelial system

The evidence that the acute phase glycoproteins of plasma are synthesized by the liver parenchymal cells is critically examined, and is found to be inconclusive. Some evidence is cited which favors the reticulo-endothelial system (RES) in general, and Kupffer cells in particular, as the site of synthesis of these proteins: 1. The entire RES contains non-glycogenic periodic acid Schiff-positive substances. 2. The diseases which affect glycoprotein levels are also known to affect the function of the RES. 3. When the animal is subjected to stress, the RES function is initially depressed and then stimulated. A similar biphasic behavior is shown by plasma glycoprotein levels. 4. Adrenal cortico-steriods are the major regulators of the RES function and of the synthesis of acute phase proteins. Moreover, both are stimulated at low concentrations, and depressed at high concentrations of the hormone. Some of the glycoproteins of the acute phase (prothrombin, the third component of complement, haptoglobin, transferrin and ceruloplasmin) have defense-related functions. The others seem to participate in phenomena like detoxification, promotion of phagocytosis, wound healing, prevention of tissue injury by lysosomal enzymes, prevention of trauma and recovery from inflammation. It is proposed that the acute phase proteins, together with antibodies, form major components of the definse system, and the RES attempts to deal with injury by mobilization of increased amounts of these substances.