Isolation of nitrogen deregulated mutants of erythromycin biosynthesis

Summary Ammonium represses erythromycin synthesis bySaccharopolyspora erythraea and insensitive mutants to this effect were isolated. Six mutants were selected and one of them produces 50% more antibiotic than the wild type in 100 mM NH₄Cl as nitrogen source. Glutamine synthetase and alanine dehydrogenase levels in the mutants were determined and no differences with wild type strain were observed.     

Knowledge-based simulation of DNA metabolism: prediction of enzyme action

We have developed a knowledge-based simulation of DNA metabolismthat accurately predicts the actions of enzymes on DNA undera large number of environmental conditions. Previous simulationsof enzyme systems rely predominantly on mathematical models.We use a frame-based representation to model enzymes, substratesand conditions. Interactions between these objects are expressedusing production rules and an underlying truth maintenance system.The system performs rapid inference and can explain its reasoning.A graphical interface provides access to all elements of thesimulation, including object representations and explanationgraphs. Predicting enzyme action is the first step in the developmentof a large knowledge base to envision the metabolic pathwaysof DNA replication and repair. Received on February 1, 1990; accepted on October 2, 1990     

Multiple xylanases of Cellulomona fimi are encoded by distinct genes

Cellulomonas fimi genomic DNA encoding xylanase activity has been cloned and expressed in Escherichia coli. As judged by DNA hybridization and restriction analysis, twelve xylanase-positive clones carried a minimum of four different xylanase (xyn) genes. The encoded enzymes were devoid of cellulase activity but three of the four bound to Avicel.     

The role of the epidermal growth factor-1 and hydrophobic stack domains of human factor IX in binding to endothelial cells.

To determine the function and specificity in factor IX of the first epidermal growth factor (EGF)-like domain and the eight-amino acid hydrophobic stack encoded by exon C (residues 39-46), these domains were replaced by the corresponding polypeptide regions of factor X and chimeric proteins were produced in human embryo kidney cells. Both chimeras were activated by factor XIa at a rate similar to plasma factor IX and exhibited calcium-dependent fluorescence quenching similar to plasma factor IX. Both chimeras competed equally for binding to the endothelial cell receptor. Our findings make it unlikely that the first EGF-like domain or the hydrophobic stack of factor IX are responsible for the specific binding of factor IX to its endothelial cell receptor.     

Recognition of complex oligosaccharides by the multi-subunit asialoglycoprotein receptor.

The hepatic asialoglycoprotein receptor, a galactose lectin, is an oligomer of two types of similar polypeptide chains, each of which weakly binds galactose. High-affinity binding of complex oligosaccharides requires a precise geometric arrangement of receptor subunits. The two subunits have different functions in receptor assembly, ligand binding and endocytosis.     

Gene mapping in marsupials: Detection of an ancient autosomal gene cluster

The genes HRAS, HBB, and CAT, which are located together on the short arm of human chromosome 11, appear to be part of a conserved synteny group found in many eutherian mammals. These genes were mapped to the chromosomes of two marsupial (metatherian) species by in situ hybridization. All three genes were located together on chromosome 3 in Macropus eugenii. Only HRAS and CAT were used to probe Dasykaluta rosamondae metaphases and these genes both mapped to chromosome 4. This suggests that the HRAS-HBB-CAT gene cluster has been conserved at least since the metatherians and eutherians diverged some 130 million years ago. These findings support the concept of a mammalian genome that has remained highly conserved throughout evolution.     

Ubiquity of Cysteine- and Metalloproteinase Activities in a Wide Range of Trypanosomatids

We have analysed the proteinase profiles of 11 species from 7 different genera of trypanosomatids by in situ detection of enzyme activities on SDS-PAGE gels containing co-polymerized gelatin as substrate, and the use of specific proteinase inhibitors. Our survey indicates that while cysteine- and metalloproteinases are distributed ubiquitously among trypanosomatids, there are marked differences between the enzyme profiles from the monogenetic (Crithidia, Herpetomonas, Leptomonas) and digenetic (Trypanosoma, Endotrypanum, Phytomonas, Leishmania) species. The detected metalloproteinase activities, ranging in size from 50–100 kDa, partitioned into the detergent-phase after Triton X-114 extraction, while most of cysteine proteinases, of three distinct molecular mass ranges (30–50 kDa, 80–100 kDa and 116–205 kDa), partitioned into the aqueous phase. Thus, within this group of organisms, the metalloproteinase activities seem to be predominantly membrane-associated proteins. We also show that the plant parasites of the genus Phytomonas exhibit a distinctive cysteine proteinase profile that might be exploited further as a criterion for taxonomy of the genus.