Previous Y chromosome studies have shown that the Cohanim, a paternally inherited Jewish priestly caste, predominantly share a recent common ancestry irrespective of the geographically defined post-Diaspora community to which they belong, a finding consistent with common Jewish origins in the Near East. In contrast, the Levites, another paternally inherited Jewish caste, display evidence for multiple recent origins, with Ashkenazi Levites having a high frequency of a distinctive, non-Near Eastern haplogroup. Here, we show that the Ashkenazi Levite microsatellite haplotypes within this haplogroup are extremely tightly clustered, with an inferred common ancestor within the past 2,000 years. Comparisons with other Jewish and non-Jewish groups suggest that a founding event, probably involving one or very few European men occurring at a time close to the initial formation and settlement of the Ashkenazi community, is the most likely explanation for the presence of this distinctive haplogroup found today in >50% of Ashkenazi Levites.
Penicillin spheroplasts of Escherichia coli were ruptured osmotically, by freezing and thawing, or mechanically. Differential centrifugation sedimented 20–30 % of the glycolytic enzymes without increasing their specific activities. There was, however, evidence of distinct groups of sedimenting enzymes; growth on different carbon sources could influence the distribution. Sucrose gradient studies gave no evidence of enzyme association but provided estimations of the molecular weight of each enzyme which were close to those subsequently observed on gel filtration. Using the determined molecular weight and a literature value for specific activity, the measured activity ratio of the enzymes was compared with that expected from an equimolar mixture. All values agreed within a factor of five, except for hexokinase. The relative roles of hexokinase and phosphotransferase in E. coli are briefly considered. An equimolar multienzyme aggregate of all the enzymes of glycolysis would have a molecular weight of about 1.6 × 106. Chromatography on a Biogel column yielded one fraction, corresponding to a molecular weight of 1.6 × 106, which contained a proportion of all the glycolytic enzyme studied, the remaining portion of each enzyme activity was eluted from the column at the position expected from its individual molecular weight. The fraction of mol. wt 1600 000 was tested for complete glycolysis pathway activity and found not to be different from a reconcentrated mixture of the separated enzymes. Both‐the eluted and the reconstructed systems showed unexpected activity changes at different protein concentrations. The specific radioactivity of pyruvate formed by these systems from [14C]glucose 6‐phosphate was reduced by the presence of unlabelled 3‐phosphoglycerate, but by less than would have been expected had the latter been able to participate fully in glycolytic activity. This result indicates that these preparations were capable of selectivity compartmenting glycolytic intermediates. Electron microscope investigation of both systems showed large numbers of regular 30 nm, diameter particles which, on disruption, appeared to be composed of smaller units: it is possible that these particles may have been aggregates containing glycolytic enzymes. The possible advantages of a glycolytic multienzyme complex are briefly discussed.
1. Repression by glucose of beta-galactosidase synthesis is spontaneously reversible in all strains of Escherichia coli examined long before the glucose has all been consumed. The extent of recovery and the time necessary for reversal differ among various strains. Other inducible enzymes show similar effects. 2. This transient effect of glucose repression is observed in constitutive (i(-)) and permease-less (y(-)) cells as well as in the corresponding i(+) and y(+) strains. 3. Repression is exerted by several rapidly metabolizable substrates (galactose, ribose and ribonucleosides) but not by non-metabolized or poorly metabolized compounds (2-deoxyglucose, 2-deoxyribose, phenyl thio-beta-galactoside and 2-deoxyribonucleosides). 4. The transient repression with glucose is observed in inducible cells supplied with a powerful inducer of beta-galactosidase synthesis (e.g. isopropyl thio-beta-galactoside) but not with a weak inducer (lactose); in the latter instance glucose repression is permanent. Diauxic growth on glucose plus lactose can be abolished by including isopropyl thio-beta-galactoside in the medium. 5. In some strains phosphate starvation increases catabolite repression; in others it relieves it. Adenine starvation in an adenine-requiring mutant also relieves catabolite repression by glycerol but not that by glucose. Restoration of phosphate or adenine to cells starved of these nutrients causes a pronounced temporary repression. Alkaline-phosphatase synthesis is not affected by the availability of adenine. 6. During periods of transient repression of induced enzyme synthesis the differential rate of RNA synthesis, measured by labelled uracil incorporation in 2min. pulses, shows a temporary rise. 7. The differential rate of uracil incorporation into RNA falls during exponential growth of batch cultures of E. coli. This is equally true for uracil-requiring and non-requiring strains. The fall in the rate of incorporation has been shown to be due to a real fall in the rate of RNA synthesis. The significance of the changes in the rate of RNA synthesis is discussed. 8. A partial model of catabolite repression is presented with suggestions for determining the chemical identification of the catabolite co-repressor itself.
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