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The OPE treatment that has been so successful in describing inclusive $\bar B \to l \bar \nu X_c$ decays yields sum rules (in particular the Uraltsev sum rule and its higher moments) implying the dominance of the $P$ wave $j_q = 3/2$ charm states in $X_c$ over their $j_q=1/2$ counterparts. This prediction is supported by other general arguments as well as quark model calculations, which illustrate the OPE results, and by preliminary lattice findings. Its failure would indicate a significant limitation in our theoretical understanding of $\bar B \to l \bar \nu X_c$. Some experimental issues have been clarified since a preliminary version of this note had appeared, yet the verdict on the composition of the final states {\em beyond} $D$, $D^*$ and the two narrow $j_q = 3/2$ resonances remains unsettled. Establishing which hadronic configurations -- $D/D^* + \pi, D/D^* + 2 \pi, ...$ -- contribute, what their quantum numbers are and their mass distributions will require considerable experimental effort. We explain the theoretical issues involved and why a better understanding of them will be of significant value. Having significant contributions from a mass continuum distribution below 2.5 GeV raises serious theoretical questions for which we have no good answer. Two lists are given, one with measurements that need to be done and one with items of theoretical homework. Some of the latter can be done by employing existing theoretical tools, whereas others need new ideas.

Glycosylation represents an attractive target for protein engineering of novel antibiotics, because specific attachment of one or more deoxysugars is required for the bioactivity of many antibiotic and antitumour polyketides. However, proper assessment of the potential of these enzymes for such combinatorial biosynthesis requires both more precise information on the enzymology of the pathways and also improved Escherichia coli-actinomycete shuttle vectors. New replicative vectors have been constructed and used to express independently the dnmU gene of Streptomyces peucetius and the eryBVII gene of Saccharopolyspora erythraea in an eryBVII deletion mutant of Sac. erythraea. Production of erythromycin A was obtained in both cases, showing that both proteins serve analogous functions in the biosynthetic pathways to dTDP-L-daunosamine and dTDP-L-mycarose, respectively. Over-expression of both proteins was also obtained in S. lividans, paving the way for protein purification and in vitro monitoring of enzyme activity. In a further set of experiments, the putative desosaminyltransferase of Sac. erythraea, EryCIII, was expressed in the picromycin producer Streptomyces sp. 20032, which also synthesises dTDP-D-desosamine. The substrate 3-alpha-mycarosylerythronolide B used for hybrid biosynthesis was found to be glycosylated to produce erythromycin D only when recombinant EryCIII was present, directly confirming the enzymatic role of EryCIII. This convenient plasmid expression system can be readily adapted to study the directed evolution of recombinant glycosyltransferases.

A 6-kb region from the chromosome of Streptomyces antibioticus, an oleandomycin producer, was cloned and sequenced. This region was located between the 3' end of the gene encoding the third subunit of the oleandomycin type I polyketide synthase and the oleP and oleB genes, which encode a cytochrome P450 monooxygenase and an oleandomycin resistance gene, respectively. Analysis of the nucleotide sequence revealed the presence of five genes encoding a cytochrome P450-like protein (oleP1), two glycosyltransferases (oleG1 and oleG2) involved in the transfer of the two 6-deoxysugars (L-oleandrose and D-desosamine) to the oleandomycin macrolactone ring, a methyltransferase (oleM1), and a gene (oleY) of unknown function. Insertional inactivation of this region by gene disruption generated an oleandomycin non-producing mutant which accumulated a compound that, according to mass spectrometry analysis, could correspond to the oleandomycin macrolactone ring (oleandolide), suggesting that the mutation affects oleandrosyl glycosyltransferase.

The gene cluster (ery) governing the biosynthesis of the macrolide antibiotic erythromycin A by Saccharopolyspora erythraea contains, in addition to the eryA genes encoding the polyketide synthase, two regions containing genes for later steps in the pathway. The region 5' of eryA that lies between the known genes ermE (encoding the erythromycin resistance methyltransferase) and eryBIII (encoding a putative S-adenosylmethionine-dependent methyltransferase), and that contains the gene eryBI (orf2), has now been sequenced. The inferred product of the eryBI gene shows striking sequence similarity to authentic beta-glucosidases. Specific mutants were created in eryBI, and the resulting strains were found to synthesise erythromycin A, showing that this gene, despite its position in the biosynthetic gene cluster, is not essential for erythromycin biosynthesis. A mutant in eryBIII and a double mutant in eryBI and eryBIII were obtained and the analysis of novel erythromycins produced by these strains confirmed the proposed function of EryBIII as a C-methyltransferase. Also, a chromosomal mutant was constructed for the previously sequenced ORF19 and shown to accumulate erythronolide B, as expected for an eryB mutant and consistent with its proposed role as an epimerase in dTDP-mycarose biosynthesis.

The production of erythromycin A by Saccharopolyspora erythraea requires the synthesis of dTDP-D-desosamine and dTDP-L-mycarose, which serve as substrates for the transfer of the two sugar residues onto the macrolactone ring. The enzymatic activities involved in this process are largely encoded within the ery gene cluster, by two sets of genes flanking the eryA locus that encodes the polyketide synthase. We report here the nucleotide sequence of three such ORFs located immediately downstream of eryA, ORFs 7, 8 and 9. Chromosomal mutants carrying a deletion either in ORF7 or in one of the previously sequenced ORFs 13 and 14 have been constructed and shown to accumulate erythronolide B, as expected for eryB mutants. Similarly, chromosomal mutants carrying a deletion in either ORF8, ORF9, or one of the previously sequenced ORFs 17 and 18 have been constructed and shown to accumulate 3-alpha-mycarosyl erythronolide B, as expected for eryC mutants. The ORF13 (eryBIV), ORF17 (eryCIV) and ORF7 (eryBII) mutants also synthesised small amounts of macrolide shunt metabolites, as shown by mass spectrometry. These results considerably strengthen previous tentative proposals for the pathways for the biosynthesis of dTDP-D-desosamine and dTDP-L-mycarose in Sac. erythraea and reveal that at least some of these enzymes can accommodate alternative substrates.

The final state\(D_s + l + \bar v_l + \cdots \) occurring inZ0-decay is analyzed, and backgrounds to the decay chain\((i) Z^0 \to B_s + \cdots ,(ii) B_s \to D_s + l + \bar v_l + \cdots \) are estimated. A resonance description is used to model the dominant source of background, and a numerical study yields estimates for the background-to-signal ratio of several per cent as input parameters are varied.

It has been shown by Finger, Horn and Mandula in the Tamm-Dancoff approximation that Coulomb exchange induces vacuum instability for α s bigger than some critical value. We show here in all generality that the critical coupling is lower using the Bogolioubov-Valatin variational method. For Coulomb exchange we find $$\tfrac{4}{3}\alpha _s^{crit} = 1$$ instead of $$\tfrac{4}{3}\alpha _s^{crit} = \tfrac{3}{2}$$ , and adding transverse gluon exchange with the Breit interaction, $$\tfrac{4}{3}\alpha _s^{crit} = \tfrac{1}{3}$$ . It is remarkable that these values of α crit are not far from the range of perturbative QCD.

In the Kobayashi-Maskawa model we compute a new contribution to the neutron electric dipole moment induced byCP violating flavour-changing transitions of the typess→d+gluon+γ through heavy quark loops. This contribution, essentially given by the triangle anomaly graph, is by itself gauge invariant. We obtain from this mechanismDn/e=3.10−32 cm, one order of magnitude below our previous estimate from usual penguin diagram contributions.

We point out that one finds in the literature two different results for the spin-orbit term in radiative transitions of hadrons. We analyze the problem and find that, besides the term usually quoted $$ - ie\omega (\sigma \times p) \cdot \varepsilon _\gamma /4m^2 \cong e[\nabla (V_v + V_s ) \times \sigma ] \cdot \varepsilon _\gamma /4m^2 $$ (V v ,V s are the Lorentz vector and scalar pieces of the binding potential and ω the photon energy), there is another term that gives as final resulte(∇V v ×σ)·eγ/2m2. We use for our proof two different approaches: the Foldy-Wouthuysen transformation, and the method of Brodsky and Primack based on a dipole formula. In hadrons, the electric field has two pieces, the photon radiation field, and a strong interaction piece, of order 1/e relative to the former. These two pieces are at the origin of the two spin-orbit terms at the order (v/c)3.

To describe the diffractive production of nonstrange mesons we use quark model harmonic-oscillator wave functions, a treatment of recoil which has proven successful forN*’S diffractive production and a determination of quark spin-flip amplitude from πN elastic-scatterings-channel centre-of-mass helicity conservation. There is no fitted parameter except the forward value and slope of the quark-quark spin-nonflip elastic amplitude deduced from πN elastic scattering. Wave function parameters were deduced from meson and baryon Regge slopes. This work is in the same line as Levin and Frankfurt and Clegg's but we think we go much further; absolute calculations are made, and we discuss which predictions are specific to quark model. We have a complete success for A2 (diffractive character, total and differential cross-sections, density matrix) and also for A3 as much as experimental comparison is possible. For A1, discussing the background puzzle, we find agreement for the total cross-section and the diffractive character of the production.

The following problem is solved: given the hypothesis of analyticity about spinor amplitudes, find an equivalent set of properties about helicity amplitudes. The method used is a rather direct one; the sets of properties gotten are not new, except for Φ(s, t)=0, when the hypothesis of saturation of the analyticity domain of the spinor amplitude is removed.