Localization of chloroplast ribosomal protein genes on Spirodela oligorhiza chloroplast DNA

Three chloroplast ribosomal protein genes have been located on Spirodela chloroplast DNA. (1) rps14 was physically mapped at the central region of the large single copy region by heterologous hybridization with the corresponding gene of Marchantia chloroplast DNA. (2) Chloroplast ribosomal protein C-S23 was detected by immunoprecipitation with a polyspecific antiserum against 30S chloroplast ribosomal proteins among the in vitro translation products of mRNAs selected by Spirodela Pstl-D chloroplast DNA fragment. (3) We have previously reported that Spirodela BamHI-G chloroplast DNA fragment encodes a 14–15 kD 50S chloroplast ribosomal protein (Posno et al. 1985 Curr Genet 9 : 211–219). Here we show that the homologous Spinacia chloroplast DNA fragment Sa1I-9 additionally directs the synthesis of another 50S chloroplast ribosomal protein in a DNA dependent E. coli cellfree system. This was confirmed by molecular weight determination, immunoprecipitation and competition immunoprecipitation experiments. mRNA selection experiments revealed that this additional chloroplast ribosomal protein gene is present on Spirodela chloroplast DNA as well, but is not expressed in the E. coli cellfree system. The identity of this 50S chloroplast ribosomal protein could not be established unambiguously, since two-dimensional gel analysis revealed that this protein comigrated, depending on the experiment, with C-L11 (26 kD) or with C-L24 (17 kD).