Cloned nodulation genes of Rhizobium leguminosarum determine host-range specificity

Summary Three nodulation-deficient (nod) mutants of Rhizobium leguminosarum were isolated following insertion of the transposon Tn5 into pRL1JI, the R. leguminosarum plasmid known to carry the nodulation genes. DNA adjacent to the nod: Tn5 alleles was subcloned and used to probe a cosmid clone bank containing DNA from a Rhizobium strain carrying pRL1JI. Two cosmid clones which showed homology with the probe contained about 10 kb of DNA in common. The R. leguminosarum host-range determinants were found to be present within this 10 kb common region since either of the cosmid clones could enable a cured R. phaseoli strain to nodulate peas instead of Phaseolus beans, its normal host. Electron microscopy of nodules induced by Rhizobium strains cured of their normal symbiotic plasmid but containing either of the two cosmid clones showed bacteroid-forms surrounded by a peri-bacteroid membrane, indicating that normal infection had occurred. Thus it is clear that this 10 kb region of nodDNA carries the genes that determine host range and that relatively few bacterial genes may be involved in nodule and bacteroid development.     

On global stability of discrete population models

A necessary and sufficient condition for the global stability of a large class of discrete population models is provided which does not require the construction of a Liapunov function. The general result is applied to difference equations defined in terms of “two hump” functions and to an example of frequency dependent selection.     

Nuclear medicine-important advances in clinical medicine: the role of nuclear and ultrasonic thyroid imaging

The Scientific Board of the California Medical Association presents the following inventory of items of progress in nuclear medicine. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established, both as to scientific fact and important clinical significance. The items are presented in simple epitome and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, research workers or scholars to stay abreast of these items of progress in nuclear medicine that have recently achieved a substantial degree of authoritative acceptance, whether in their own field of special interest or another.The items of progress listed below were selected by the Advisory Panel to the Section on Nuclear Medicine of the California Medical Association and the summaries were prepared under its direction.     

Metabolism of 4-pentenoic acid and inhibition of thiolase by metabolites of 4-pentenoic acid

The metabolism of 4-pentenoic acid, a hypoglycemic agent and inhibitor of fatty acid oxidation, has been studied in rat heart mitochondria. Confirmed was the conversion of 4-pentenoic acid to 2,4-pentadienoyl coenzyme A (CoA), which either is directly degraded via beta-oxidation or is first reduced in a NADPH-dependent reaction before it is further degraded by beta-oxidation. At pH 6.9, the NADPH-dependent reduction of 2,4-pentadienoyl-CoA proceeds 10 times faster than its degradation by beta-oxidation. At pH 7.8, this ratio is only 2 to 1. The direct beta-oxidation of 2,4-pentadienoyl-CoA leads to the formation of 3-keto-4-pentenoyl-CoA, which is highly reactive and spontaneously converts to another 3-ketoacyl-CoA derivative (compound X). 3-Keto-4-pentenoyl-CoA is a poor substrate of 3-ketoacyl-CoA thiolase (EC 2.3..1.16) whereas compound X is not measurably acted upon by this enzyme. The effects of several metabolites of 4-pentenoic acid on the activity of 3-ketoacyl-CoA thiolase were studied. 3,4-Pentadienoyl-CoA is a weak inhibitor of this enzyme that is protected against the inhibition by acetoacetyl-CoA. The most effective inhibitor of 3-ketoacyl-CoA thiolase was found to be 3-keto-4-pentenoyl-CoA, which inhibits the enzyme in both a reversible and irreversible manner. The reversible inhibition is possibly a consequence of the inhibitor being a poor substrate of 3-ketoacyl-CoA thiolase. It is concluded that 4-pentenoic acid is metabolized in mitochondria by two pathways. The minor yields 3-keto-4-pentenoyl-CoA, which acts both as a reversible and as a irreversible inhibitor of 3-ketoacyl-CoA thiolase and consequently of fatty acid oxidation.     

ACTIVATION OF PIG BRAIN GLUTAMINASE

Pig brain glutaminase (EC 3.5.1.2, l -glutamine amidohydrolase) is activated by certain anions (e.g. phosphate, fluoride, carboxylic acids) and inhibited by others (e.g. chloride, bromide, iodide and glutamate). The only cation which has been found to activate the enzyme is the ammonium ion. This applies to both the tris-HCl form and the phosphate-borate form of glutaminase.     

Über bau und funktion der prosoma-drüsen von spinnmilben (Tetranychidae,Trombidiformes)

Zoomorphology - Die licht- und elektronenmikroskopische Untersuchung der Prosomadrüsen der Spinnmilben Bryobia praetiosa, Bryobia rubrioculus und Tetranychus urticae (Tetranychidae,...