Characterization of an RNA-binding protein gene (RBPA) in the cyanobacterium Synechococcus SP. PCC 7942

Many species of cyanobacteria possess genes whose products contain an RNP motif that is highly similar to that found in the RNP family of eukaryotic RNA-binding proteins. The rbpA gene, one of two RNA-binding protein genes in Synechococcus sp. PCC 7942, codes for a protein of 107 amino acids with a single RNA Recognition Motif (RRM) and a short (23 aa) auxiliary domain containing 15 glycine residues. Mutation of rbpA by insertional inactivation using the Sm/Sp resistance omega cassette resulted in a reduction in doubling time and an alteration of the whole cell spectrum when compared with the wild type organism. This phenotype was not observed in a "control mutant" in which the omega cassette was inserted outside the rbpA gene. We were unable to rescue the mutant phenotype by insertion of a copy of the rbpA gene into a neutral site in the cyanobacterial genome. However, the I)NA fragment cloned in the neutral site did not include a palindromic sequence located in the 3' untranslated region of the gene. We think that this sequence may" play a role in expression of the gene; we are currently testing this hypothesis. The function of :yanobacteriaJ RNA-binding proteins is not known. Our preliminary findings suggest that the RbpA protein may affect the content of the phycobilisome :omponents of the photosynthetic apparatus. The nature or identity of the RNA molecules that are bound by these proteins is also not known: binding tudies to identify specific RNA sequences which inay bind to this protein re underway. (Research supported by the Natural Sciences and Engineering Research Council of Canada).