Cloning, purification and characterisation of a recombinant purine nucleoside phosphorylase from Bacillus halodurans Alk36

A purine nucleoside phosphorylase from the alkaliphile Bacillus halodurans Alk36 was cloned and overexpressed in Escherichia coli. The enzyme was purified fivefold by membrane filtration and ion exchange. The purified enzyme had a Vmax of 2.03 × 10−9 s −1 and a Km of 206 μM on guanosine. The optimal pH range was between 5.7 and 8.4 with a maximum at pH 7.0. The optimal temperature for activity was 70°C and the enzyme had a half life at 60°C of 20.8 h

DeoR repression at-a-distance only weakly responds to changes in interoperator separation and DNA topology.

The interoperator distance between a synthetic operator Os and the deoP2O2-galK fusion was varied between 46 and 176 bp. The repression of the deoP2 directed galK expression as a function of the interoperator distance (center-to-center) was measured in vivo in a single-copy system. The results show that the DeoR repressor efficiently can repress transcription at all the interoperator distances tested. The degree of repression depends very little on the spacing between the operators, however, a weak periodic dependency of 8-11 bp may exist

Purification and characterization of the deoR repressor of Escherichia coli.

The deoR gene, which encodes the deor repressor protein in Escherichia coli, was fused to the strong Ptrc promoter in plasmid pKK233-2. The Ptrc promoter is kept repressed by lacI repressor to prevent cell killing. Induction of the Ptrc--deoR fusion plasmid resulted in the accumulation of 4% of the soluble protein as deoR protein. The deoR repressor protein was purified to 80% purity using conventional techniques; it has a mass of 28.5 kd and appears to exist as an octamer in solution. The deoR repressor is shown by DNase I footprinting to bind to the 16 bp palindromic sequence in the Pribnow box region of the deoP1 promoter. Also, the deoR repressor binds cooperatively in vitro to a DNA template with two deoR binding sites separated by 224 bp in keeping with the conclusion from genetic experiments that more than one operator is required for efficient repression of the deo operon