Molecular analysis of fatty acid desaturation of Spirulina platensis C1: Study of regulation of the desA gene expression
1997
Supapon Cheevadhanarak | Morakot Tanticharoen | Suchada Chaisawadi | Dauenpen Meesapyodsuk | Amporn Suphatrakul | Patcharaporn Deshnium(National center for Genetic Engineering and Biotechnology, Bangkok (Thailand))
Important mechanism of the cyanobacterial cells in responses to decrease in temperature is the extent of levels of unsaturated fatty acids in membrane lipids. In Spirulina platensis C1, fatty acid desaturation is involved by three enzymes, namely, delta9, delta12 and delta6 desaturases. In this study, we examined the effects of low temperature on the expression of the desA gene for delta12 desaturase using Northern blot analysis. Two types of mRNAs (at the sizes of 1.5 and 1.7 kb) were hybridized with the desA probes of S. platensis C1. However, the 1.7-kb mRNA was present in low abundance. The 5 ends of the desA mRNAs were mapped by primer extension analysis, and two transcriptional start sites were detected, locating at 208 and 246 bases upstream of the open reading frame of the desA gene. By analysis of the nucleotide sequence around 3 end of the desA gene, two identical terminators were found at 233 and 373 bases downstream of the stop codon. These findings indicate that two species of the desA transcripts were produced by a single desA gene that is controlled by two distinct promoters. When the temperature was shifted from 35 deg C (growth temperature) to 22 deg C, the levels of both types of mRNA rapidly increased, and remained at these levels for 10 min after the shift. Then, the transcripts started to level off to about half of the original levels after 15 min of the shift. Addition of rifampicin, an inhibitor of transcription, 20 min prior to the temparature down shift inhibited the accumulation of the desA transcripts. This suggests that an increase in mRNA levels of the desA gene is related to the transcriptional induction of the desA gene rather than the increase in mRNA stability.
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