Introduction

The structure and function of higher plant chloroplast genomes have been studied extensively in recent years.It is well established that chloroplast DNA（ct-DNA）exists in circular form and has an average contour length of 50 μm corresponding to a molecular weight of 108 daltons（Bedbrook and Kolodner，1979）.This circular molecule is divided into four regions：two inverted repeats separated by a small and a large single-copy region（Bedbrook and Kolodner，1979）.The inverted repeats contain the genes for ribosomal and transfer RNAs while the single-copy region contains the genes for various proteins and tRNAs（Steinmetz et al.，1978）.Potentially，ct-DNA has a coding capacity for up to 150 polypeptides of 4×104 daltons each（Kung，1977）.To date only a few proteins coded by ct-DNA and synthesized in isolated chloroplasts have been identified（Ellis，1981）.They are，for example，the large subunit（LS）of ribulose 1，5-bisphosphate carboxylase-oxygenase（RuBPCase）（Kung，1976），several subunits of coupling factor（Nelson et al.，1980），cytochrome f（Doherty and Gray，1979），elongation factor G and T（Ciferri et al.，1979），cytochrome b559（Zielinski and Price，1980），Dicyclohexylcarbodiimide-binding protein（Doherty and Gray，1980）and apoprotein of chlorophyll-protein complex 1（Zielinski and Price，1980）.

Y.S.Zhu，E.J.Duvall，P.S.Lovett，and S.D.Kung，Department of Biological Sciences，University of Maryland Baltimore County，Catonsville，MD 21228，USA

Offprint requests to：S.D.Kung.(https://www.daowen.com)

此文发表于1982年“Mol.Gen.Genet”187：61-66.

The site of coding information for the polypeptides mentioned above was determined by genetic or biochemical approaches.The direct method for testing the coding capacity of chloroplast genomewould be to clone the entire chloroplast genome and then test for the expression of each clone.To achieve this we have cloned the entire Nicotiana otophora chloroplast genome in E.coli and tested each cloned ct-DNA fragment for expression in E.coli cells.In this communication we report the construction of a clone library and present a restriction map of N.otophora chloroplast genome including the localization of genes for rRNA and the LS of RuBPCase.Finally，we demonstrate that certain cloned ct-DNA fragments direct the synthesis of chloroplast DNA-directed polypeptides in E.coli.