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(36), but VP1 is essential for formation of infectious AAV type 2 (AAV-2) particles (17, 42, 50). VP2 cotransports VP3 into the nucleus before capsid assembly (18,36). VP3 alone also forms capsids but only when targeted to the nucleus (18). Encapsidation of the AAV-2 genome likely occurs in the nucleoplasm in areas where capsids, Rep proteins, and DNA colocalize (52). Detailed analysis of the protein-protein interactions of Rep and VP proteins favors a model by which Rep-tagged DNA initiates packaging by interaction with capsid proteins (11). Several of the above-mentioned studies of the AAV-2 capsid assembly process were aided by using monoclonal antibodies (MAbs) directed against the capsid proteins.AAV-2 infects a broad range of cells by binding to its primary receptor, heparan sulfate proteoglycan (47). Two types of coreceptors, ␣ v ␤5 integrin and fibroblast growth factor receptor

Cysteine synthesis in bacteria and plants is catalyzed by serine acetyltransferase (SAT) and O-acetylserine (thiol)-lyase (OAS-TL), which form the hetero-oligomeric cysteine synthase complex (CSC). In plants, but not in bacteria, the CSC is assumed to control cellular sulfur homeostasis by reversible association of the subunits. Application of size exclusion chromatography, analytical ultracentrifugation, and isothermal titration calorimetry revealed a hexameric structure of mitochondrial SAT from Arabidopsis thaliana (AtSATm) and a 2:1 ratio of the OAS-TL dimer to the SAT hexamer in the CSC. Comparable results were obtained for the composition of the cytosolic SAT from A. thaliana (AtSATc) and the cytosolic SAT from Glycine max (Glyma16g03080, GmSATc) and their corresponding CSCs. The hexameric SAT structure is also supported by the calculated binding energies between SAT trimers. The interaction sites of dimers of AtSATm trimers are identified using peptide arrays. A negative Gibbs free energy (⌬G ‫؍‬ ؊33 kcal mol ؊1 ) explains the spontaneous formation of the AtCSCs, whereas the measured SAT:OAS-TL affinity (K D ‫؍‬ 30 nM) is 10 times weaker than that of bacterial CSCs. Free SAT from bacteria is >100-fold more sensitive to feedback inhibition by cysteine than AtSATm/c. The sensitivity of plant SATs to cysteine is further decreased by CSC formation, whereas the feedback inhibition of bacterial SAT by cysteine is not affected by CSC formation. The data demonstrate highly similar quaternary structures of the CSCs from bacteria and plants but emphasize differences with respect to the affinity of CSC formation (K D ) and the regulation of cysteine sensitivity of SAT within the CSC.Cysteine biosynthesis in plants and bacteria is catalyzed by a two-step process. Serine acetyltransferase (SAT 2 ; EC 2.3.1.30) activates serine by transfer of the acetyl moiety from acetyl coenzyme A to form O-acetylserine (OAS). Then OAS accepts sulfide by catalysis of OAS (thiol)-lyase (OAS-TL; EC 2.5.1.47). This fixation of free sulfide from assimilatory sulfate reduction or external sulfide sources is the exclusive entry of reduced sulfur into cellular metabolism. SAT and OAS-TL form the hetero-oligomeric cysteine synthase complex (CSC). In enterobacteria and plants, the interaction of SAT and OAS-TL is stabilized by the presence of sulfide, although the addition of OAS dissociates the two enzymes (1, 2). Plant and bacterial OAS-TLs are dimers that are catalytically inactive in the CSC but become fully active upon dissociation of the complex by OAS (1, 3). However, these properties do not seem to relate to metabolic regulation of cysteine synthesis in enterobacteria. In Escherichia coli, regulation of cysteine synthesis is mainly achieved by control of the cysteine regulon that includes OAS-TL and the genes encoding for proteins catalyzing sulfate uptake and reduction but not bacterial SAT. Bacterial SAT is constitutively expressed but strongly inhibited by cysteine (K I ϭ 1.1 M cysteine). In the presence of cysteine, SAT of E. coli...

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We have analyzed and compared the circadian locomotor activity rhythms of Drosophila melanogaster and D.pseudoobscura. The rhythms of D.pseudoobscura are stronger and the periods shorter than those of D.melanogaster. We have also transformed D.melanogaster flies with a hybrid gene containing the coding region of the D.pseudoobscura period (per) gene. Behavioral assays of flies containing this hybrid gene show that the per protein encoded by the D.pseudoobscura per gene is able to rescue the rhythmic deficiencies of arrhythmic, pero1 D.melanogaster. More important, the rhythms of some of these strains are stronger and the periods shorter than those of D.melanogaster (and those of transformants which carry the equivalent D.melanogaster per gene construct) and hence resemble those of D.pseudoobscura. The results suggest that the primary amino acid sequence of the per gene encodes species‐specific behavioral instructions that are detectable when only the per gene is transferred to a different species.