Decay of mRNAs for Bacteriochlorophyll and Caroten...
Particular Bam HI restriction fragments ofthe R'plasmid pRPS404 have been mapped genetically and shown to contain predominantly crt（in BamHI-H，-M，-G，-J）or bch（in BamHI-E，-D）genes（see Figure 1）［31，41］.We used these DNA fragments as probes for dot hybridization to determine how the levels of mRNA for pigment biosynthetic enzymes change during the O2 shift，and we observed a broad range of responses.The kinetics of mRNA decay was similar to that for the LH and RC proteins when the fragments BamHI-E（bchD，bchG，and bchJ）and BamHI-J（crtF，crtE，and an unidentified，heavily transcribed gene）［39］were used as probes（see Figure 8）.In contrast，the level of mRNAs from the Bam HI-D fragment（bch F，bch K，and bch H）decreased during the first 20 min after the shift and then increased in the next 40 min（see Figure 8）.In general，the levels of mRNA from fragments containing crt genes increased relative to that of mRNA for RC and LH during the shift from anaerobic to aerobic conditions.An increase in total mRNA level was found for the BamHI M fragment（data not shown），which only contains the crtE gene based on genetic［4，31］and our unpublished DNA sequencing data.The level of mRNA hybridizing to the BamHI G fragment（crtC，crtD）decreased，but to a far smaller extent than the mRNAs for LH，RC，and bacteriochlorophyll biosynthetic enzymes.The increased mRNA level was most noticeable for the Bam HI H fragment containing the crtA gene；it reached a maximum of about two fold 1 h after the shift（see Figure 8）.Although the Bam HI H fragment has been mapped to contain other genes，we attribute this response mainly to the crtA gene，since the significant stimulation of mRNA by O2 was not observed in the crt transposon mutant KZR9A12（data not shown）.
Figure 8 Time course of mRNA levels for bacteriochlorophyll and carotenoid biosynthetic enzymes in photosynthetic cells.Photosynthetic cells were subjected to proflavin and O2 treatments as in Figure 7.The probes used for dot hybridization were pBR325 plasmids containing the Bam HI-E，-J，-D，and-H fragments.These clones and the genes harbored in these clones are listed in Table 1.The arrows underneath BamHI refer to the vertical axis for each set of measurements(https://www.daowen.com)
