The expression of HBsAg gene in yeast under GAL-10 promoter control

The surface antigen gene of HBV (adr subtype) is inserted into the YEP 1 which is replicated and selected in E. coli and baker yeast Saccharomyces cerevisiae. The HBsAg gene can be expressed in yeast under GAL-10 promoter control. The protein synthesized in yeast is assembled into particles that have the same size and shape as particles isolated from plasma. One microgram surface antigen can be yielded in 100 ml culture.

The yeast plasmid 2mu circle encodes components required for its high copy propagation

The yeast plasmid 2mu and certain hybrid plasmids constructed from it are maintained stably and at high copy number in yeast cells. By examining various mutant hybrid 2mu plasmids, we show that these properties require the integrity of four plasmid loci. Two of these, designated REP1 and REP2, are active in trans and correspond to two open coding regions of 2mu. The other two loci are active only in cis and correspond to the origin of replication and to a region, designated REP3, located several hundred bp away from the origin and consisting of direct repeats of a 62 bp sequence. We propose that the REP loci constitute a copy control system that overrides normal cellular restriction on plasmid replication and amplifies the plasmid when copy number is low.

Liposomal uptake of microcrystalline benzo(a)pyrene studied with synchronous fluorescence

Synchronous fluorescence spectrometry is employed for kinetic studies of benzo(a)pyrene uptake by phospholipid bilayers. It provides several advantages over the conventional mode. These include less background interferences, higher sensitivity, and relatively independent of dynamic quenching by paramagnetic ions. The rate limiting step in benzo(a)pyrene uptake appears to be a first order process not controlled by diffusion. Signal enhancement upon successive increments of liposomes decreases as if it is dependent on the number of free microcrystals in solution.

Differentiation of Actinomyces propionicus from Actinomyces israelii and Actinomyces naeslundii by gas chromatography

Gas–liquid chromatography (g.l.c.) was used for the analysis of certain metabolic end products of Actinomyces propionicus, as an aid in the separation of this organism from the morphologically similar Actinomyces species, A. israelii and A. naeslundii. Profiles of the chromatograms for the major volatile acids of five strains of A. propionicus studied were found to be distinct from those of four strains of A. israelii and four strains of A. naeslundii. The ratio of propionic acid to acetic acid was approximately 50 times as great for A. propionicus as for the other Actinomyces species. Formic acid was present in significant amounts in both A. israelii and A. naeslundii, but was present only in trace amounts in A. propionicus.Two major nonvolatile acids, lactic and succinic, were identified for the A. israelii and A. naeslundii strains. One of the A. propionicus strains also showed both acids in significant amounts; however, the other four strains of A. propionicus showed succinic acid in large amounts, but only trace amounts of lactic acid.