The biogenesis of chloroplast has been described in great detail. However, the transcriptional activities of this DNA have not been described, and very little is known about transcriptional regulation of organelle gene expression. The proposed research will be concentrated on the following problems: 1) We will construct a detailed map of chloroplast DNA transcription on the level of individual transcription units. Cloned fragments of chloroplast DNA, EM techniques and S1 nuclease mapping will be used. We hope to determine the structure of transcriptional units, the level of their expression at various stages of cell development. We will also determine if split genes are present in chloroplast genome. 2) We will locate the exact positions of chloroplast ribosomal genes on the physical map of DNA. The technique of heterologous hybridization with cloned E. coli ribosomal genes will be used. 3) The location of other genes involved in translation or transcription of genetic information of chloroplast will be determined using the same technique. 4) We will clone the appropriate chloroplast DNA fragments and establish a cloned library of this genome. This will facilitate the determination of which genes are encoded in chloroplast DNA and how their expression is regulated.