| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2005: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2004: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
In chloroplasts, most genes, are transcribed by plastid-encoded plastid RNA polymerase (PEP). PEP is a multi-subunit RNA polymerase, whose catalytically core enzyme consists of the plastid-encoded subunits. The promoter-specific transcription initiation requires assembly of a nuclear-encoded s factor to the core. PEP s factors belong to a super family of E.coli s^<70> and recognize two consensus hexamers of plastid promoter, -10 and -35 elements through region 2.4 and 4.2, respectively. In Arabidopsis, there have been identified six genes for s factors, Sig1 to 6. In this research, we focus our attention to the following two subjects.
1.Mutational analysis of selective promoter recognition of SIG5
Blue light responsive promoter of psbD, psbDBLRP is recognized only by SIG5 among six SIGs. To reveal the mechanism of the selective recognition property of SIG5, we established a method to assay the activity of SIG5 to recognize psbDBLRP using transient over expression of SIG5 in protoplasts p
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repared from the sig5 deletion mutant of Arabidopsis thaliana. Using this method, we examined the effect of point mutation for amino acids in various regions of SIGS on the activity and found that an amino acid in region 4.2, N484, which is not involved in the binding to -35 element was essential for SIG5 to recognition psbDBLRP. The substitution of other amino acids in region 4.2 and 2.4 of SIG5, including the amino acids involved in the binding to -10 and -35 elements to the corresponding amino acids in SIG1 that can not recognize psbDBLRP, hardly affected the activity of SIG5.
2.Analysis of light induced transcription of six sig genes in Arabidopsis thaliana
The light induced transcription of six SIG genes in Arabidopsis taliana, was examined focusing on the effects of wave length and strength of light. SIG1 and SIG5 were found to be distinct from other SIG genes in their rapid response to light. The rapid induction of SIG5 transcripts was differently regulated by two types of cryptochrome, cry1 and cry2, depending on the light strength, while the rapid induction of SIG1 transcripts was mediated both through cry1-dependent and cryptochrome-independent pathways. Less
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