Cloning, sequencing, and expression of UDP-glucose pyrophosphorylase gene from Acetobacter xylinum BRC5

A UDP-glucose pyrophosphorylase (UGPase) gene from Acetobacter xylinum BRC5 has been cloned, sequenced, and expressed in Escherichia coli. The gene consists of 867 nucleotides and encodes a polypeptide of 289 amino acid residues with a calculated molecular mass of 31,493 Da. The amino acid sequences of the enzyme showed an 85.8% identity to those of an enzyme from A. xilinum ATCC 23768. A polyhistidine-UGPase fusion enzyme was expressed and purified from the transformed E. coli. The enzyme showed a 35,620-Da single protein band on SDS/PAGE and an about 160,000-Da protein band on 8-16% pore-gradient polyacrylamide gel, indicating the enzyme may be a tetramer or pentamer composed of four or five identical subunits. Kinetic analysis of the enzyme showed a typical Michaelis-Menten substrate saturation pattern, from which Km and Vmax were calculated to be 3.22 mM and 175.4 micromol x min(-1) x mg(-1) for UDP-glucose and 0.24 mM and 69.4 micromol x min(-1) x mg(-1) for PPi, respectively, required Mg2+ for maximal activity, and was inhibited by free pyrophosphate. Computer-aided comparison of the Acetobacter enzyme sequence with those of other bacterial enzymes found significant similarities among them and predicted that Lys84 is a catalytically important residue. Lys84 in the enzyme, which was also conserved in other bacterial enzyme sequences, was replaced by arginine or leucine. The K84R mutant enzyme was successfully expressed in E. coli and showed enzyme activity (63% of the wild-type enzyme activity), but K84L was not isolated in stable form. These results suggest that Lys84 is significant in not only catalysis but also maintenance of the active structure.

Activation of the thymidine kinase promoter by herpes simplex virus type 1 immediate early proteins

The herpes simplex virus type 1 (HSV-1) thymidine kinase (TK) gene promoter contains binding sites for the cellular transcription factors such as Spl, CTF, and TFIID, each of which affects basal level expression of the TK gene. The transcription of the TK gene was induced by viral immediate early proteins, ICP0 and ICP4 in an additive manner, but was repressed by ICP22 and ICP27. To gain further insights into the role of ICP0 and ICP4 for expression of the TK gene during virus infection, several mutants with deletions or point mutations in each of the transcriptional regulatory elements were generated starting at -109 and progressing toward +1. According to the CAT assay involving these mutants, the cellular transcription factor (CTF) binding site was necessary for efficient expression in the presence of transfected ICP0 and ICP4 or during virus infection, whereas the Sp1 binding site had a minor effect on ICP0-mediated TK expression. These results indicate that the immediate early proteins of HSV-1 regulate expression of the TK gene during virus infection by modulating activities of cellular transcription factors such as CTF.

Expression of a non-inactivating K+ channel driven by a rat heat shock promoter increased the resting potential in Aplysia silent neurons

We assessed the role of a non-inactivating K+ channel (aKv5.1) in the resting potential by overexpressing this channel by heat shock in the neurons. A reporter gene lacZ linked to a promoter region spanning from the -285 to the +88 base of the rat HSP70ib gene was induced 62.5-fold when this DNA construct was microinjected into the neurons of the marine mollusk Aplysia and treated with heat shock at 30 degrees C for 3 h. Using this efficient induction system, we induced the expression of aKv5.1 by heat shock in cultured, electrically silent neurons of Aplysia and examined its effect on the resting potential. The channel expression increased the resting potential by approximately 10 mV. This increase was specific to heat shock induction and abolished by treatment with TEA, a specific K+ channel blocker. These results provide the direct evidence that a low voltage-activated, non-inactivating K+ channel can contribute to the resting potential.