Study on the function of RNA0binding proteins of cyanobcteria and chloroplasts

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1. RNA-binding proteins, Rbp1 and Rbp2, of the unicellular cyanobacterium Synechococcus sp, strain PCC6301 are localized in cytosol and bind RNA molecules in vivo. To elucidate their functions, gene-disruption experiments were performed. The experiments indicated that disruption of rbpl gene is lethal while rbp2 gene is not essential under normal growth condition. We are currently identifying the target RNA species of Rbp proteins.2. To clarify the function of chloroplast RNA-Binding proteins (cpRNPs), effect of the cpRNPs on pre-mRNA processing was assayd. When cpRNPs were removed from in vitro assay system, processing of pre-mRNA was enhanced. This suggests that cpRNPs may take part in mRNA processing as negative regulator.3. cDNA2s encoding RNA-binding proteins, RZ-1 and RGP-3, have been isolated from a Nicotiana sylvestris cDNA library. The deduced amino acid sequences revealed that RZ-1 contains a consensus sequence-type RNA-binding domain (CS-RBD) and a zinc finger motif of the CCHC type, and RGP-3 has a CS-RBD and a short glycine-rich sequence. RZ-1 is localized in the nucleoplasm of tobacco cultured cells. Glycerol gradient fractionation of tobacco nuclear lysates showed the tRZ-1 is associated with a large ribonucleoprotein particle of 60 S in size. This suggests that RZ-1 may be involved in pre-mRNA processing. RGP-3 is localized as 10S particles in nucleoplasm. The biochemical basis of the RNA specificity and of ribonucleoprotein particles is an interesting issue, and further experiments are necessary to elucidate the function of RZ-1 and RGP-3.