Physiological Characterization of RNA-Binding Protein-Deficient Cells from Synechococcus sp. Strain PCC7942

The unicellular cyanobacteria, Synechococcus sp. strains PCC7942and PCC6301, have two small RNA-binding proteins, Rbp1 and Rbp2.In this study, native gel electrophoresis of the nuclease-treatedSynechococcus cell extracts showed that both Rbps are associatedin vivo with RNA but not with DNA. This indicates that theyare bona fide RNA-binding proteins. To address the functionof Rbps, we have characterized the mutants deficient in Rbp1or Rbp2. The Rbp1 deficient cells showed the same growth curve,cell color and cell viability as the wild-type strain at 30°C.The Rbp2-less mutant also grew well as wild-type but exhibiteda yellow-green color, and its cell viability was significantlyreduced. On exposure of the Rbp1-deficient mutant cells to atemperature of 10°C for one week, cell viability was completelylost. Western blot analysis showed that Rbp1 increases onlyin response to a temperature shift from 30 to 10°C, whereasRbp2 accumulates at a constant rate at cold temperature. Interestingly,translation elongation factor Tu was significantly decreasedin Rbp2-deficient cells but not in Rbp1-deficient cells. Thus,each Rbp appears to have a distinct role in cellular function. (Received June 28, 1999; Accepted September 24, 1999)