Sterigmatocystin — incidence, fate and production byA versicolor in ras cheese

Sterigmatocystin (STG) is a toxic metabolite produced by severalAspergillus species. Because of its toxic and carcinogenic properties the occurrence of STG in food is considered to represent a potential hazard to man. The present study was designed to investigate following points:

Transfection of genes encoding the T cell receptor-associated CD3 complex into COS cells results in assembly of the macromolecular structure

The T cell antigen receptor (TCR) consists of a disulfide-linked TCR-alpha/beta heterodimer that is both structurally and functionally associated with a set of four non-covalently linked membrane proteins termed CD3-gamma, -delta, -epsilon, and -zeta. An additional protein described recently, CD3-omega, has been suggested to play a role in assembly of the CD3 complex on the basis of its transient association with the CD3 proteins early during biosynthesis. Association of all the proteins seems to be a prerequisite for intracellular transport, since mutants lacking either the TCR-alpha or -beta protein do not express the CD3 complex on the cell surface. CD3-cDNAs were transfected into COS cells in order to study the protein-protein interactions ruling the assembly of the CD3 macromolecular structure. CD3-delta-epsilon, CD3-gamma-epsilon, and CD3-gamma-delta-epsilon intermediates could be detected. These data indicated that a CD3 core structure could be formed in the absence of the other members of the complex (CD3-zeta, -omega, TCR-alpha, and -beta). Both the individual CD3 chains and the assembled CD3.gamma.delta.epsilon complexes could not be detected on the cellular surface but in an intracellular compartment, probably the endoplasmic reticulum or the cis Golgi. The transfection experiments allowed us to identify the 25-kDa member of the murine CD3 complex as CD3-epsilon m. Furthermore, a 23-kDa glycoprotein seen upon metabolic labeling of human T cells was shown to be an immature form of the CD3-gamma h protein.     

Mechanism of translational coupling between coat protein and replicase genes of RNA bacteriophage MS2.

We have analyzed the molecular mechanism that makes translation of the MS2 replicase cistron dependent on the translation of the upstream coat cistron. Deletion mapping on cloned cDNA of the phage shows that the ribosomal binding site of the replicase cistron is masked by a long distance basepairing to an internal coat cistron region. Removal of the internal coat cistron region leads to uncoupled replicase synthesis. Our results confirm the model as originally proposed by Min Jou et al. (1). Activation of the replicase start is sensitive to the frequency of upstream translation, but never reaches the level of uncoupled replicase synthesis.     

Evidence that the phytochrome gene family in black cottonwood has one PHYA locus and two PHYB loci but lacks members of the PHYC/F and PHYE subfamilies

The phytochrome photoreceptors play important roles in the photoperiodic control of vegetative bud set, growth cessation, dormancy induction, and cold-hardiness in trees. Interestingly, ecotypic differences in photoperiodic responses are observed in many temperate- zone tree species. Northern and southern ecotypes of black cottonwood (Populus trichocarpa Torr. & Gray), for example, exhibit marked differences in the timing of short-day-induced bud set and growth cessation, and these responses are controlled by phytochrome. Therefore, as a first step toward determining the molecular genetic basis of photoperiodic ecotypes in trees, we characterized the phytochrome gene (PHY) family in black cottonwood. We recovered fragments of one PHYA and two PHYB using PCR-based cloning and by screening a genomic library. Results from Southern analyses confirmed that black cottonwood has one PHYA locus and two PHYB loci, which we arbitrarily designated PHYB1 and PHYB2. Phylogenetic analyses which included PHY from black cottonwood, Arabidopsis thaliana and tomato (Solanum lycopersicum) suggest that the PHYB/D duplications in these species occurred independently. When Southern blots were probed with PHYC, PHYE, and PHYE heterologous probes, the strongest bands that we detected were those of black cottonwood PHYA and/or PHYB. These results suggest that black cottonwood lacks members of the PHYC/F and PHYE subfamilies. Although black cottonwood could contain additional PHY that are distantly related to known angiosperm PHY, our results imply that the PHY family of black cottonwood is less complex than that of other well-characterized dicot species such as Arabidopsis and tomato. Based on Southern analyses of five black cottonwood genotypes representing three photoperiodic ecotypes, substantial polymorphism was detected for at least one of the PHYB loci but not for the PHYA locus. The novel character of the PHY family in black cottonwood, as well as the differences in polymorphism we observed between the PHYA and PHYB subfamilies, indicates that a number of fundamental macro- and microevolutionary questions remain to be answered about the PHY family in dicots.