Border formation in a Bmp gradient reduced to single dissociated cells.

Conversions of signaling gradients into sharp "all-or-none" borders are fundamental to tissue and organismal development. However, whether such conversions can be meaningfully reduced to dissociated cells in culture has been uncertain. Here we describe ultrasensitivity, the phenomenon equivalent to an all-or-none response, in dissociated neural precursor cells (NPCs) exposed to bone morphogenetic protein 4 (Bmp4).

Phosphoglucose isomerase from Escherischia coli K 10: purification, properties and formation under aerobic and anaerobic condition.

Phosphoglucose isomerase has been purified from crude extracts of Escherichia coli K 10. Two forms of the enzyme were separated during the purification procedure. The major species comprises more than 90% of the enzyme activity, has an apparent molecular weight of about 125,000 and consists of two 59,000 molecular weight subunits; the minor species has an apparent size of 230,000 and consists of (possibly four) subunits of 59,000 molecular weight.

Phenotypic suppression of a fructose-1,6-diphosphate aldolase mutation in Escherichia coli.

Strain NP 315 of Escherichia coli possesses a thermolabile fructose-1, 6-diphosphate (FDP) aldolase; its growth on carbohydrate substrates is inhibited probably as a consequence of the accumulation of high intracellular levels of FDP. Studies of one class of phenotypic revertants of strain NP 315 which have regained their ability to grow on C(6) substrates at 40 C showed that in these strains the buildup of the inhibitory FDP pool is prevented by additional mutations in enzymes catalyzing the conversion of the substrate offered in the medium to FDP. For example, mutations affecting 6-phosphogluconate dehydrogenase activity (gnd(-)) may be selected in great number without any mutagenesis and enrichment simply by isolating revertants of strain NP 315 able to grow on gluconate at 40 C.