| Summary: | Thesis (Ph. D.), Memorial University of Newfoundland, 1999. Biochemistry Bibliography: p. 258-279 Many species of cyanobacteria possess genes whose products are highly similar to the RNP family of RNA-binding proteins found in eukaryotes. This work describes the characterization of rbpA, one of two RNA-binding protein {rbp) genes now known to exist in the unicellular cyanobacterium Synechococcus sp. PCC 7942. This gene codes for a protein of 107 amino acids. It contains a single RNA Recognition Motif (RRM) as well as an auxiliary domain rich in glycine residues. -- Mutation of the rbpA gene by insertional inactivation using the spectinomycin resistance omega cassette resulted in a temperature-sensitive phenotype with an altered pigment composition when compared with the wild type organism. This phenotype was not observed in a "control mutant", in which the omega cassette was inserted outside of the rbpA gene. Complementation experiments demonstrated that it was possible to rescue the phenotype of the "knock-out" mutant by insertion of a wild type copy of the rbp A gene into a neutral site in the cyanobacterial genome. -- The function of cyanobacterial RNA-binding proteins is not known. A histidine-tagged form of RbpA (HeRbpA) was purified using metal chelate affinity chromatography. RNA binding experiments demonstrated that this protein showed a preference for poly(A), poly(G) and poly(U) RNA but not poly(C). This specificity did not appear to be significantly affected by removal of the auxiliary domain. Overall, work presented here suggests that the RbpA protein may affect content of the phycobilisome components in the photosynthetic apparatus. It also appears to be a protein which is required for growth at lower temperatures.
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