Hanbury Brown-Twiss Correlations for a Driven Superatom.

Hanbury Brown-Twiss interference and stimulated emission, two fundamental processes in atomic physics, have been studied in a wide range of applications in science and technology. We study interference effects that occur when a weak probe is sent through a gas of two-level atoms that are prepared in a singly excited collective (Dicke or "superatom") state and for atoms prepared in a factorized state. We measure the time-integrated second-order correlation function g^{(2)} of the output field as a function of the delay τ between the input probe field and radiation emitted by the atoms and find that, for the Dicke state, g^{(2)} is twice as large for τ=0 as it is for γ_{e}τ≫1 (γ_{e} is an excited state decay rate), while for the product state, this ratio is equal to 3/2. The results agree with those of a theoretical model in which any effects related to stimulated emission are totally neglected-the coincidence counts measured in our experiment arise from Hanbury Brown-Twiss interference between the input field and the field radiated by the atoms.

SUC1 gene of Saccharomyces: a structural gene for the large (glycoprotein) and small (carbohydrate-free) forms of invertase.

Saccharomyces cerevisiae revertant strain D10-ER1 has been shown to contain thermosensitive forms of the large (glycoprotein) and small (carbohydrate-free) invertases and a very low level of the small enzyme, along with a wild-type level of the large form (T. Mizunaga et al., Mol. Cell. Biol. 1:460-468, 1981). These characteristics cosegregated in crosses of the revertant strain with wild-type sucrose-fermenting (SUC1) or nonfermenting (suc0) strains. In addition, there is tight linkage between sucrose and maltose fermentation in revertant D10-ER1 (characteristic of the SUC1 and MAL1 genes). From this we infer that a single reversion event is responsible for the several changes observed in D10-ER1, and that this mutation maps within or very close to the SUC1 gene present in the ancestor strain 4059-358D. The revertant SUC1 allele in D10-ER1 (termed SUC1-R1) was expressed independently of the wild-type SUC1 gene when both were present in diploid cells. Diploids carrying only the wild-type or the mutant genes synthesized invertases with the characteristics of the parental Suc+ haploids. The possibility that a modifier gene was responsible for the alterations in the invertases of revertant D10-ER1 was ruled out by appropriate crosses. We conclude that SUC1 is a structural gene that codes for both the large and the small forms of invertase and suggest that SUC2 through SUC5 are structural genes as well.

Temperature-sensitive forms of large and small invertase in a mutant derived from a SUC1 strain of Saccharomyces cerevisiae.

Mutagenesis of the sucrose-fermenting (SUC1) Saccharomyces cerevisiae strain 4059-358D yielded an invertase-negative mutant (D10). Subsequent mutagenic treatment of D10 gave a sucrose-fermenting revertant (D10-ER1) that contained the same amount of large (mannoprotein) invertase as strain 4059-358D but only trace amounts of the smaller intracellular nonglycosylated enzyme. Limited genetic evidence indicated that the mutations in D10 and D10-ER1 are allelic to the SUC1 gene. The large invertases from D10-ER1 and 4059-358D were purified and compared. The two enzymes have similar specific activity and Km for sucrose, cross-react immunologically, and show the same subunit molecular weight after removal of the carbohydrate with endo-beta-N-acetylglucosaminidae H. They differ in that the large enzyme from the revertant is rapidly inactivated at 55 degrees C, whereas that from the parent is relatively stable at 65 degrees C. The small invertase in extracts of D10-ER1 is also heat sensitive as compared to the small enzyme from the original parent strain. The low level of small invertase in mutant D10-ER1 may reflect increased intracellular degradation of this heat-labile form. In several crosses of D10-ER1 with strains carrying the SUC1 or SUC3 genes, the temperature sensitivity of the large and small invertases and the low cellular level of small invertase appeared to cosegregate. These findings are evidence that SUC1 is a structural gene for invertase and that both large and small forms are encoded by a single gene. A detailed genetic analysis is presented in a companion paper.

ZENK induction in the zebra finch brain by song: Relationship to hemisphere, rhythm, oestradiol and sex.

Oestradiol is abundant in the zebra finch auditory forebrain and has the capacity to modulate neural responses to auditory stimuli with specificity as a result of both hemisphere and sex. Arrhythmic song induces greater ZENK expression than rhythmic song in the caudomedial nidopallium (NCM), caudomedial mesopallium (CMM) and nucleus taeniae (Tn) of adult zebra finches. The increases in the auditory regions (i.e. NCM and CMM) may result from detection of errors in the arrhythmic song relative to the learned template. In the present study, zebra finches were treated with oestradiol, the aromatase inhibitor fadrozole or a control and then exposed to rhythmic or arrhythmic song to assess the effect of oestradiol availability on neural responses to auditory rhythms. ZENK mRNA was significantly greater in the left hemisphere within the NCM, CMM and Tn. Main effects of sex were detected in both auditory regions, with increased ZENK in males in the NCM and in females in the CMM. In the CMM, an effect of hormone treatment also existed. Although no pairwise comparison was statistically significant, the pattern suggested greater ZENK expression in control compared to both fadrozole- and oestradiol-treated birds. In the NCM, an interaction between sex and hormone treatment suggested that the sex effect was restricted to control animals. An additional interaction in the NCM among sex, stimulus rhythmicity and hemisphere indicated that the strongest effect of laterality was present in males exposed to arrhythmic song. The hormone effects suggest that an optimal level of oestradiol may exist for processing rhythmicity of auditory stimuli. The overall pattern for left lateralisation parallels the left lateralisation of language processing in humans and may suggest that this hemisphere is specialised for processing conspecific vocalisations. The reversed sex differences in the NCM and CMM suggest that males and females differentially rely on components of the auditory forebrain for processing conspecific song.

Phosphatidylseryl-transfer RNA in Bacillus licheniformis 749/C.

Phosphatidylserine has been found in extracts of Bacillus licheniformis made under alkaline conditions but not under neutral or acidic ones and was derived from the tRNA fraction. In tRNA preparations kept below neutrality during purification, phosphatidylserine was the only phospholipid released when the pH was raised to 9.0. The amount of bound phosphatidylserine could be increased by incubating tRNA from B. licheniformis or Escherichia coli with CTP and phosphatidic acid in the presence of an S-30 extract from either organism. The tRNA carrying phosphatidylserine has been separated from the bulk of the tRNA by DEAE-Sephadex chromatography in the presence of a detergent. On deaminoacylation of this material and rechromatography on DEAE-Sephadex, a number of peaks were found, indicating that this behavior is not confined to a single isoaccepting species.

Vesicle penicillinase of Bacillus licheniformis 749/C. Apparent identity with the plasma membrane enzyme.

A substantial fraction of the total membrane penicillinase of Bacillus licheniformis 749/C is attached to the vesicles released during conversion of the cells to protoplasts. This enzyme was purified since there was indirect evidence that it differed from the enzyme that remained with the protoplast. The purified vesicle penicillinase has the same molecular weight and general properties as the plasma membrane (protoplast) enzyme and, similarly, contains a covalently linked phosphatidylserine residue. Treatment of the two enzymes with trypsin produced phosphatidylserine-containing peptides which could not be distinguished by gel or paper electrophoresis. The two membrane penicillinases are very similar, if not identical.

Membrane associated phospholipoproteins of Bacillus lichenformis 749.

The membrane-bound penicillinase of Bacillus licheniformis 749/C is a phospholipoprotein that differs from the hydrophilic exoenzyme in that its polypeptide chain carries an additional 25 residues (mostly hydrophilic) with phosphatidylserine as the NH2-terminus. To determine if other phospholipoproteins are present in the plasma membrane, the penicillinase-inducible strain 749 was grown without inducer in the presence of [2-(3)H] glycerol. Electrophoretic separation of the membrane proteins (after removal of free lipids) showed an association of 3H-activity with certain of the proteins which could not be broken by lipid solvents and strongly denaturing conditions. Pronase digestion of the membrane proteins (after solvent extraction) released phosphatidylserine, thus indicating the covalent linkage of protein and phospholipid. Treatment of the isolated membranes with trypsin solubilized the protein portion of some of the phospholipoproteins (as with penicillinase), but not the 3H-labelled fragment. Penicillinase should be considered as the first observed example of a group of phosphatidylserine-containing proteins present in the plasma membrane of B. licheniformis 749 and 749/C.

Action of cytochalasin A, a sulfhydryl-reactive agent, on sugar metabolism and membrane-bound adenosine triphosphatase of yeast.

Cytochalasin A at 10-20 mug/ml inhibits growth and sugar uptake by Saccharomyces strain 1016. The effects of cytochalasin A in intact cells were completely prevented when 1 mM cysteine or dithiothreitol was added along with cytochalasin A, but were not eliminated by thiols added after inhibition had occurred. Purified yeast hexokinase, glucose-6-P dehydrogenase, phosphofructokinase and aldolase were not sensitive to cytochalasin A (20 mug/ml). Glyceraldehyde-3-P dehydrogenase was strongly inhibited by cytochalasin A (5 mug/ml); activity was promptly restored by thiols. Anaerobic glycolysis was inhibited by cytochalasin A or by iodoacetate; unlike iodoacetate, cytochalasin A did not cause accumulation of sugar phosphates. In contrast, cytochalasin A, but not iodoacetate, inhibited isolated membrane-bound ATPases. Cytochalasin A is a sulfhydryl-reactive agent and has membrane-related effects (adenosine triphosphatase) which may well be the basis of its interference with energy-dependent uptake of solutes.

Large and small invertases and the yeast cell cycle. Pattern of synthesis and sensitivity to tunicamycin.

We have examined the pattern of synthesis of the glycoprotein form of invertase and of the smaller carbohydratefree from in synchronous culture to obtain further infromation concerning their biosynthetic relationship. Saccharomyces mutant 1710 was chosen since its invertase production is almost completely derepressed during growth in 0.1 M mannose medium. The large enzyme, unlike the small form, binds to concanavalin A-Sepharose, and on this basis the two types can conveniently be separated for analysis. Large invertase was produced throughout the cell cycle. Synthesis of the small invertase was periodic; the single burst occurred at or close to the budding stage. Tunicamycin, which inhibits the sypthesis of external glycoproteins, halted formation of the large enzyme but not of the small form, and there was no accumulation of invertase activity with the properties of the small enzyme. Hence, it is unlikely that the small form is a precursor of the large one. Despite marked differences in their amino acid compositions, the two enzymes have many similarities. They are probably, in part, the products of the same gene(s), and the differences between them may largely reflect differences in post-translational processing.

Microheterogeneity in yeast invertase.

Yeast external invertase (EC 3.2.1.25), a glycoenzyme consisting of equal parts by weight of protein and mannan, has been found to contain covalently bound phosphate. Three preparations (from two yeast strains) had mannose/PO4 ratios of 31-35, equivalent to 24-27 PO4 residues per mol of enzyme, while a fourth had only 7 PO4 residues per mol. From one of the high-PO4 enzymes, approx. 69% of the phosphorus was recovered as mannose 6-phosphate. No correlation was found between invertase activity and phosphorus content. The PO4 contents of the invertases exceeded those of the cell wall mannans from the respective yeasts. Thus, contamination of the invertases by cell wall phosphomannan is unlikely. Electrofocusing of the low-PO4 invertase yielded four components with pI values from 3.96 to 4.40, and yeast internal invertase (a mannan- and PO4-free, cytoplasmic isozyme) was isoelectric at approx. pH 4.5. The high-PO4 invertase was considerably more heterogeneous, with two major species of pI 3.65 and 3.32 and a highly acidic component of pI smaller than 2.7; however, the mannose/PO4 ratio of each species was approximately the same. PO4-gradient elution from hydroxyapatite resolved the high-PO4 invertase into five isozymes of increasing acidity and mannan content. Since the mannose/PO4 ratios of these invertase species are constant, the increase in the mannan/protein (and, therefore PO4/protein ratio is apparently responsible for the microheterogeneity of phosphoinvertase.23

Differential transcription of the bla regulatory region during induction of beta-lactamase in Bacillus licheniformis.

Induction of beta-lactamase (blaP) in Bacillus licheniformis involves the regulatory genes blaI (repressor), blaR1 (coinducer) and R2 (function unknown). Transcription of the bla genes during induction was followed by Northern hybridization. In the first 30 min 2.3-kb transcripts encoding blaI and blaR1 were present. Subsequently, blaP mRNA and short transcripts encoding only blaI accumulated and reached a peak at 1 h. All bla transcripts turn over rapidly. Active repressor is not required for the burst of blaI-blaR1 mRNA. The production of blaI-blaR1 mRNA, and thus of BlaR1, is probably controlled both at initiation of transcription and at a later step in its synthesis and degradation.

Repressor gene, blaI, for Bacillus licheniformis 749 beta-lactamase.

The repressor gene, blaI, for the beta-lactamase of Bacillus licheniformis 749 was functional when cloned in Escherichia coli, but addition of a beta-lactam did not lead to induction. One plasmid contained fragments from the inducible strain (source of repressor), the other carried fragments from the blaI- mutant 749/C (target). blaI lies just 5' to the promoter for the structural gene, blaP, and the target is the promoter region between the two genes. Interaction with both promoters seemed necessary for full repression. BlaI is a hydrophilic protein (Mr 15036) with the some structural similarities to repressors from Gram-negative bacteria.

Accumulation of glyceride-modified pre-penicillinase of Bacillus licheniformis in Escherichia coli treated with globomycin.

The membrane penicillinase of Bacillus licheniformis is a glyceride-cysteine lipoprotein whose NH2 terminus is analogous to the major outer membrane lipoprotein of Escherichia coli. When E. coli cells producing B. licheniformis penicillinase were treated with the antibiotic, globomycin, a precursor of the penicillinase, pre-penicillinase, accumulated in the cell. It could be immunoprecipitated with anti-penicillinase antibodies; it contained palmitate; and one of its two cysteine residues was modified by glycerol. The action of globomycin, probably indirectly, also activates protease which acts differently on the pre-penicillinase than does the signal peptidase. The results strongly indicate that the pre-penicillinase is processed by the globomycin-sensitive signal peptidase in E. coli, and the modification of precursor by lipid precedes removal of the signal peptide as it does with the membrane lipoproteins of E. coli.

Bacillus cereus 569/H beta-lactamase I: cloning in Escherichia coli and signal sequence determination.

The gene, penPC, for beta-lactamase I of Bacillus cereus 569/H has been cloned and its expression studied in Escherichia coli. The protein product from the in vitro translation of penPC was shown by gel electrophoresis to have an Mr of 36 000 which is larger than the in vivo products found in B. cereus and E. coli. The DNA sequence of the signal region was determined. It revealed that the smallest known mature form present in B. cereus culture fluids is preceded by 45-48 amino acids in pre-beta-lactamase I, considering that there are 3 initiation codons in the same reading frame, one or more of which might be initiating translation. Unlike the Bacillus licheniformis 749/C beta-lactamase, which has a membrane-bound thioether lipoprotein form, the single Cys residue in the B. cereus beta-lactamase I signal sequence is unmodified and a single processed form of the enzyme is present in E. coli cells carrying penPC.

Interaction of BlaI, the repressor for the beta-lactamase gene of Bacillus licheniformis, with the blaP and blaI promoters.

BlaI repressor for the beta-lactamase gene (blaP) of Bacillus licheniformis 749, was shown to repress expression of blaP and of the repressor gene (blaI), using the purified protein in a DNA-directed in vitro translation assay. Binding of BlaI to the promoter regions of blaP and blaI was examined by equilibrium and competitive binding assays. BlaI binds to the blaP promoter with an equal or only slightly higher affinity than to the blaI promoter. DNase I footprinting shows that BlaI binds directly to the blaP and blaI promoters, such that RNA polymerase binding and/or transcript elongation would be blocked.

Expression in Escherichia coli of the carboxy terminal domain of the BLAR sensory-transducer protein of Bacillus licheniformis as a water-soluble Mr 26,000 penicillin-binding protein.

A cloning vector has been constructed which allows production and export by Escherichia coli of the Met346-Arg601 carboxy terminal domain of the 601 amino acid BLAR sensory-transducer involved in beta-lactamase inducibility in Bacillus licheniformis. The polypeptide, referred to as BLAR-CTD, accumulates in the periplasm of E. coli in the form of a water-soluble, Mr 26,000 penicillin-binding protein. These data and homology searches suggest that BLAR has a membrane topology similar to that of other sensory-transducers involved in chemotaxis.