EXPRESSION OF HEAT SHOCK GENES HSP16.6 AND HTPG IN THE CYANOBACTERIUM, SYNECHOCYSTIS SP. PCC 6803
Heat shock proteins (HSP) are found in all living organisms in response to elevated temperatures, and protect cells from heat damage. In this dissertation, hsp16.6 and htpG were studied in the cyanobacterium, Synechocystis sp. PCC 6803. The hsp16.6 transcriptional start point was positioned 44 base pairs (bp) upstream of ATG translation start codon. A reporter vector was constructed by ligating the 265 bp upstream fragment onto the upstream region of the lacZ coding sequence. Galactosidase analysis indicated the 265 bp region did not induce lacZ gene expression in E. coli; although lacZ expression was induced when the Synechocystis groESL promoter was used. In Synechocystis cells, lacZ was expressed when the 265 bp fragment was used as a promoter. Cold stress and ethanol did not induce lacZ expression, while heat shock, salt stress, sorbitol, hydrogen peroxide and high light induced lacZ. Deletions of the 265 bp region demonstrated that the induction of galactosidase activity was lost when a region upstream of the transcriptional start point was deleted. The htpG null mutant was obtained by inserting a chloramphenicol resistance cassette (Cmr) in the htpG coding sequence. The htpG null mutant, hsp16.6 null mutant, and the double mutant cells grew well at 30°C and 37°C, but not at 40°C. This suggests that HtpG and HSP16.6 proteins do not have an essential role at normal and mildly elevated temperatures. Cell growth, cell survival rate, and oxygen electrode measurements demonstrated that htpG mutant, hsp16.6 mutant, and double mutant cells were sensitive to heat stress. Decreased basal and acquired thermotolerance were observed when mutants were heat shocked, with double mutant cells being the most sensitive. A comparison of mutants showed that hsp16.6 mutant was more sensitive to heat shock than htpG mutant. In summary, a 265 bp region upstream of hsp16.6 was demonstrated to response to heat shock, salt stress, sorbitol, hydrogen peroxide and high light, and the deletion of a region upstream of the transcriptional start point resulted in the loss of heat induction. HtpG was demonstrated to be essential during heat stress, and the deletion of htpG caused decreased basal and acquired thermotolerance.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:heat shock cyanobacteria synechocystis htpg hsp16 6 regulation reporter promoter basal thermotolerance acquired
Date of Publication:01/01/2003