On the Organization and Affinities of the Amoeba,Pompholyxophrys punicea Archer,Based on Ultrastructural Examination of Individual Cells from Wild Material1

The genus Pompholyxophrys includes amoebae which have a spherical body, fine radiating pseudopodia, and a layer of adhering siliceous “perles.” These organisms are normally regarded as a type of heliozoon. Ultrastructural examination of P. punicea reveals that those characters associated with well characterized heliozoa, such as microtubular axonemes and extrusomes, are lacking. The species has much in common with nucleariid filose amoebae with which it, and the related genus Pinaciophora, are regarded as having affinities. The species P. punicea is rare, and this study was made possible by the application of techniques developed for the ultrastructural examination of single cells. The assessment of protistan diversity and interrelationships relies heavily on the use of ultrastructural characters. Although techniques that are based on the examination of a small number of individual cells have limitations, they do allow rare organisms to be included in the re-evaluation of protistan systematics.     

Isolation and culture of smooth muscle cells from human umbilical cord arteries

Summary A short method is described for obtaining a large number of pure vascular smooth muscle cells in culture. The smooth muscle cells were isolated from human umbilical cord arteries digested twice by an enzyme mixture of collagenase, trypsin, elastase, and DNAase with addition of α-tosyl-lysyl chloromethane. Primary cell culture and first subculture were not contaminated by endothelial cells, no Factor VIII being produced. The cultures consisted of smooth muscle cells as appeared from phase contrast and electron microscopy. Part of this study was supported by a scholarship from the Dutch Ministry of Education and Science and by the Leyden University Foundation.     

Dependence of secretion and assembly of type 1 fimbrial subunits of Escherichia coli on normal protein export.

The export of fimbrial subunits was found to be diminished at the restrictive temperature in a strain bearing a secA(Ts) mutation. Likewise, export was inhibited in a strain harboring a malE-lacZ protein fusion upon induction of hybrid protein synthesis. Both conditions resulted in the accumulation of a precursor protein ca. 2,000 daltons larger than the mature fimbrial subunit.     

Simultaneous release of penicilloic acid and phenylacetyl glycine by penicillin-binding proteins 5 and 6 of Escherichia coli.

Penicillin-binding proteins (PBPs) 5 and 6 of Escherichia coli released the bound penicilloyl moiety at an intermediate rate relative to, e.g., Staphylococcus aureus PBPs 4 (rapid) and 1 or 2 (slow). Each of these E. coli PBPs released the bound penicilloyl moiety as both penicilloic acid (hydrolysis) and phenylacetyl glycine (scission of the C-5--C-6 bond followed by hydrolysis).     

Molecular cloning and genetic organization of C4-dicarboxylate transport genes from Rhizobium leguminosarum.

Cosmids containing C4-dicarboxylate transport (dct) genes were identified from a gene bank of Rhizobium leguminosarum DNA made in the broad-host-range vector pLAFR1 by their ability to complement R. trifolii dct mutants. The dct genes were further characterized by subcloning, restriction site mapping, and transposon Tn5 and Tn7 mutageneses. Three dct loci were identified within a 5.5-kilobase region of DNA, in the order dctA-dctB-dctC. The results suggested that dctA encoded a structural component necessary for C4-dicarboxylate transport, whereas dctB and dctC encoded positive regulatory elements, and that dctA was transcribed divergently from dctB and dctC. Expression of dctA and dctC was obtained from vector promoters in some pLAFR1- and pSUP106-based plasmids.     

Protoplast forming ability in the genusBrevibacterium

Formation of protoplasts and their reversion were followed in 7 strains of brevibacteria. The formation of protoplasts and their reversion differed both between various species of brevibacteria and between various mutant strains of the same species.     

Identification of the purC gene product of Escherichia coli.

The purC region of the Escherichia coli chromosome was isolated from in vivo-derived lambda transducing bacteriophages and cloned in high-copy-number plasmids. The product of the purC gene, phosphoribosylaminoimidazolesuccinocarboxamide synthetase, was identified as a protein with an Mr of ca. 27,000. The level of the protein is increased by more than 60-fold in strains carrying the gene on a high-copy-number plasmid. Purine addition represses the enzyme level in both plasmid- and non-plasmid-containing strains.