| Three translational fusions with lacZ were constructed using the cpcBA, apcAB and psaAB promoter regions from cyanobacterium, Synechococcus sp. PCC 7002. The construction pAQE19AP (containing the apcAB promoter) was shown to have no detectable {dollar}beta{dollar}-galactosidase activity in the cyanobacterial strain G38. Therefore no useful information could be obtained from this construction in the {dollar}beta{dollar}-galactosidase assays. {dollar}beta{dollar}-galactosidase activities were determined for the fusion plasmids pAQE19LPC (with the cpcBA promoter) and pAQE19PSA (with the psaAB promoter) under a variety of environmental stress conditions, including variable light intensity and nutrient deprivation.; The {dollar}beta{dollar}-galactosidase assays revealed that as light intensity decreased, the level of cpcBAC and psaAB activity increased. In the nutrient limitation assays, cpcBAC and psaAB activity levels decreased in response to nitrogen, carbon, and, to a lesser extent, phosphorus starvation. Iron and sulfur starvation had no affect on phycocyanin levels within the cell as measured by whole cell absorption spectra analysis.; To confirm these results, mRNA levels for a variety of genes were qualitatively analyzed by Northern blot hybridization using total RNA extracts from cultures grown under the same conditions as those used in the {dollar}beta{dollar}-galactosidase assays. The levels of mRNA obtained with cpcBA probes confirmed the {dollar}beta{dollar}-galactosidase assay results. Other gene fragments from cpcBACDEF, cpcG, apcABC, apcD, apcE, apcF, psaAB, psaC, psaE, psbA1, psbB, psbC, psbD1, psbD2, and recA were also used as probes to determine whether a particular gene was nitrogen sensitive or responded to changes in light intensity. The 5{dollar}spprime{dollar} endpoints of the transcripts of these genes were also mapped by primer extension. The data obtained from both the Northern blot hybridizations and the analysis of the sequences upstream of the mapped endpoints were used to attempt to categorize the potential promoter sequences obtained. In general, the non-nitrogen regulated genes had an E. coli-like consensus promoter sequence while the nitrogen regulated gene sequences could not be placed into any category of known sigma factor recognition sequences nor were they similar to other cyanobacterial promoter regions. The fact that there are at least three (probably more) categories of promoters in Synechococcus sp. PCC 7002 suggest the presence of multiple sigma factors for RNA polymerase. |
