Regulation of phycobilisome rod proteins and mRNA at different light intensities in the cyanobacterium Synechococcus 6301.

The regulation of the light-harvesting antennae, the phycobilisome (Pbs), and the cpcB1A1-cpcH-cpcI-cpcD operon encoding the structural proteins of the Pbs rod, was studied in the cyanobacterium, Synechococcus sp. PCC 6301, when grown at different light intensities (li). Pbs were purified and their linker protein (LP) profiles analyzed on SDS-polyacrylamide gels. At increasing li, the amount of the distal 30-kDa LP decreased prior to any change in the amount of the proximal 33-kDa LP, indicating a sequential increase in the Pbs rod length. While the amount of LP in the rod decreased with increasing li, the levels of the LP mRNAs increased. Post-transcriptional regulation of the expression of the polycistronic cpcB1A1-cpcH-cpcI-cpcD mRNA was inferred from these observations. The half-life of the mRNAs studied was typically found to be 7 min with four exceptions: (1 and 2) the half-lives for the 3.4- and 3.7-kb polycistronic LP mRNAs were 16 and 1 min at the low (lli) and high li (hli), respectively; (3) the half-life of the 1.4-kb cpcB1A1 mRNA was 2 min at lli; and (4) the 1.3-kb cpcB1A1 transcript had a half-life of 10 min at lli. At hli, it was found that the 1.3-kb cpcB1A1 transcript did not start to disappear until the amount of the 1.4-kb cpcB1A1 transcript had reached the level equal to that of the 1.3-kb mRNA, implying that the 1.4-kb transcript might be processed to the 1.3-kb form.