In chloroplasts, transcription of plastid genes is mediated by two types of RNA polymerase: plastid-encoded RNA polymerase (PEP) and nuclearencoded RNA polymerase (NEP) . Transcription in plastids is also mediated by a number of nuclear-encoded factors in addition to PEP and NEP. In the insoluble RNA polymerase preparation samples, a total of 18 components named as pTACs (pTAC1 to pTAC18) were identified. pTAC18 (AT2G32180) is one of the components associated with PEP complex.
