CO-TRANSCRIPTION PATTERN OF AN INTROGRESSED OPERON IN THE MAIZE CHLOROPLAST GENOME COMPRISING 4 ATP SYNTHASE SUBUNIT GENES AND THE RIBOSOMAL RPS2

Several examples of the introduction of a gene from one gene complex i nto another (introgression) are found when chloroplast RP gene cluster s are compared to those in Escherichia coli or cyanobacteria. Here we describe the transcript pattern of one such cluster from maize (Zea ma ys) that includes the genes for 4 subunits of the thylakoid ATP syntha se (atpI, H, F, A) and the rps2 gene. Twelve transcript species coveri ng the size range from 7000 to 800 nt were identified in RNA isolated from dark-grown and greening maize seedlings, and several of them were characterized by reverse transcription analysis. A major species of 6 200 nt, with its 5' end at 181 nt upstream of the initiating ATG of rp s2, contained the transcripts of all the 5 genes. Two further sets of transcripts having their 5' ends ca. 120 and 50 nt upstream of the ini tiation codons of the atpI and atpH genes were also identified. Thus, this plastid gene cluster in maize is functionally organized as an ope ron with additional regulatory features to allow for increased accumul ation of mRNAs for the thylakoid components.