Studies on protein multimers. The association-dissociation behaviour of -galactosidase in glycerol

Development of combinatorial bioengineering using yeast cell surface display--order-made design of cell and protein for bio-monitoring

A genetic system to display proteins as their active and functional forms on the cell surface of yeast, Saccharomyces cerevisiae, has been exploited. Surface-engineered (arming) cells displaying amylase or cellulase could assimilate starch or cellulose as the sole carbon source, although S. cerevisiae can not intrinsically assimilate them. Arming cells with a green fluorescent protein (GFP) from Aequorea victoria can emit green fluorescence from the cell surface in response to the environmental conditions. From these results, we attempted to construct a system to monitor the foreign protein production in yeast by simultaneous displaying the enhanced GFP (EGFP). The expression in yeast of the Escherichia coli beta-galactosidase-encoding gene was examined as an example of intracellular production and that of the human interferon-alpha (omega, IFN-omega)-encoding gene as an example of extracellular production. Their productions and the simultaneous surface-display of EGFP as a reporter were controlled by the same promoter, GAL1. The relationship among fluorescence signals and their productions was evaluated. The surface-display system, unlike one using tag-proteins, would be able to facilitate the monitoring of native protein productions in bioprocesses using living cells in real time by the combination of promoters and GFP variants.

Quantitation of insertion sequence IS10 transposase gene expression by a method generally applicable to any rarely expressed gene

We have found that IS10 transposase is synthesized in tiny amounts, about 0.15 polypeptide chain per cell per generation on average, as judged from the beta-galactosidase activity of a single chromosomal copy of a suitable transposase-lacZ gene fusion. Enzymatic activity from the fusion gene is a factor of 10 lower in a permeabilized whole cell assay than in cell extracts. Probably, most cells contain fewer than four polypeptide chains, and these chains can assemble into active tetramers only after cell disruption. This interpretation permits formulation of two equations relating enzyme activities to transcription and translation rates, solution of which reveals that the fusion gene is expressed at the average rate of only 0.25 transcript per cell per generation, with an average of only 0.58 translation product per transcript. This methodology is generally applicable to analysis of any gene from which fewer than four polypeptide chains are synthesized per cell per generation.

Evidence for an active dimer of Escherichia coli beta-galactosidase

BETA-Galactosidase (EC 3.2.1.23), prepared from strains ML 308 and K12 3300 of Escherichia coli, dissociated into an inactive monomer in the presence of Ag+. When such a monomer preparation is treated with excess of thiol an enzymically active dimer is formed in addition to an active tetramer. It is suggested that Ag+ may be of value in studies on other multimeric proteins as a mild dissociating agent.