This chapter describes the components of the transcriptional apparatus in plastids (RNA polymerases, promoters, transcription factors) and their roles in transcription. The chromosomes of plastids from nearly all plants contain genes for core subunits of PEP, a bacterial-type RNA polymerase which might be responsible for transcription of all plastid genes in algae but shares responsibility for transcription with one or more nuclear encoded transcriptases (NEP) in higher plants. There is increasing evidence that the catalytic subunit of NEP is related to RNA poly-merases of bacteriophages like T7. NEP and PEP are active throughout leaf development. Transcription of plastid genes and operons by multiple promoters is common. Promoter recognition by PEP is mediated by a-factors. Factors supporting NEP in promoter binding are not known yet. Examples of regulation of transcription are described demonstrating promoter selection by a-factors and activation/repression of gene activity by transcription factors.
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