THE 2 RNA-POLYMERASES ENCODED BY THE NUCLEAR AND THE PLASTID COMPARTMENTS TRANSCRIBE DISTINCT GROUPS OF GENES IN TOBACCO PLASTIDS

The plastid genome in photosynthetic higher plants encodes subunits of an Escherichia coli-like RNA polymerase (PEP) which initiates transcr iption from E. coli sigma(70)-type promoters. We have previously estab lished the existence of a second nuclear-encoded plastid RNA polymeras e (NEP) in photosynthetic higher plants, We report here that many plas tid genes and operons have at least one promoter each for PEP and NEP (Class II transcription unit). However, a subset of plastid genes, inc luding photosystem I and II genes, are transcribed from PEP promoters only (Class I genes), while in some instances (e.g. accD) genes are tr anscribed exclusively by NEP (Class III genes). Sequence alignment ide ntified a 10 nucleotide NEP promoter consensus around the transcriptio n initiation site, Distinct NEP and PEP promoters reported here provid e a general mechanism for group-specific gene expression through recog nition by the two RNA polymerases.