Interactions between the Escherichia coli cyclic AMP receptor protein and RNA polymerase at class II promoters

The effects of a number of mutations in crp have been measured at different cyclic AMP receptor protein (CRP)-dependent Class II promoters, where the CRP-binding site is centred around 41 1/2 base pairs upstream from the transcription start point. The amino acid substitutions HL159 and TA158 result in reduced CRP-dependent activation, but the reduction varies from one Class II promoter to another. Deletions in the C-terminus of the RNA polymerase alpha subunit suppress the effects of HL159 and TA158. The role of the C-terminus of alpha at these promoters is assessed. Other changes at E58, K52 and E96 affect CRP activity specifically at Class II promoters and their role is discussed.

Mapping the cAMP receptor protein contact site on the alpha subunit of Escherichia coli RNA polymerase

The C-terminal region (amino acid residues 236-329) of the Escherichia coli RNA polymerase alpha subunit carries the contact site I for positive transcription factors. For detailed mapping of the contact site for the cAMP receptor protein (CRP), we made a library of mutant rpoA by polymerase chain reaction (PCR) mutagenesis, such that each should carry a single mutation on average and exclusively in the C-terminal half of the rpoA gene, and then screened this library for mutants with decreased expression of the lacZ gene. Reconstituted holoenzyme containing the mutant alpha subunits transcribed galP1 but not lacP1 in vitro in the presence of cAMP-CRP. DNA sequence determination of several 'Lac-' mutant rpoA genes revealed that all had mutations clustered within a short segment near the C-terminus of alpha, between amino acid residues 265 and 270. A cluster of contact sites appear to exist within the contact site I region, each comprising of about five amino acids and responding in molecular communication with a different transcription factor(s).

The role of oxygen free radicals in myocardial ischemia/reperfusion injury

A series of experiments have been done to investigate the role of oxygen free radicals in ischemia/reperfusion injury. The following results were found: Myocardial MDA content increased significantly after post-ischemic reperfusion in vivo and in vitro. A blockade of the xanthine oxidase pathway for free radical generation could provide effective protection against ischemia/reperfusion injury. Exogenous reactive oxygen intermediates H2O2, .OH and O2- could induce changes in the contractility and electrophysiological properties of myocardial cells similar to those seen in ischemia/reperfusion. An outburst of free radical generation was detected by ESR spectroscopy at low temperature (-173 degrees C) and with the spin trapping technique during the very early phase of reperfusion. The authors emphasize the important role of free radicals in the pathogenesis of myocardial ischemia/reperfusion injury.

NAD+ analogs in formation of new fluorophores on ultraviolet irradiation with D-glyceraldehyde-3-phosphate dehydrogenase

A number of NAD+ analogs have been tested in their ability to form fluorescent derivatives when UV irradiated with the active site Cys-149 carboxymethylated GAPDH and this has been compared with their properties of acting as hydrogen acceptors and forming the Racker band. Among the analogs tested, NHD+, NGD+, APAD+ and epsilon NAD+ give positive results in all the above-mentioned reactions whereas alpha NAD+, NMN+ and CPAD+ are all negative. FPAD+ forms a fluorescent derivative on UV irradiation with the carboxymethylated enzyme but is inactive as a hydrogen acceptor and does not form the Racker band. This is probably due to thiohemiacetal formation of the pyridine 3-aldehyde of this derivative with the active site SH group required for both the latter 2 reactions. TPAD+, although active active as a hydrogen acceptor, does not form either a fluorescent derivative or a Racker band. The fact that for the great majority of the analogs, the property of forming fluorescent derivatives is in parallel with their hydrogen acceptor activity seems to show that the formation of the fluorescent derivative is indeed at the active site, and hence can be used as an intrinsic probe for the study of the conformation of the active site of this enzyme.