Genes for Biosynthesis of Bchl and Crt

The genes for pigment biosynthesis were transcribed at lower levels than those for LH and RC subunits，but they were responsive to light intensity and O2 concentration，as measured by dot blot analysis.Although the changes in Bchl content in response to light and O2 roughly corresponded to the levels of the LH and RC mRNAs（data not shown），the changes in the levels of mRNA for Bchl and Crt biosynthetic enzymes had the following features（see Figure 2，Table 2）.①Under high light intensity，the amounts of mRNAs of bch genes（bchJ，-G，-D，-H，-K，and-F）located in the BamHI-E and BamHI-D fragments showed a slight but reproducible decrease，whereas the amounts of mRNAs of crt genes（crtC，-D，-A，-I，and-B）carried by the BamHI-H，BamHI-G，and BamHI-M fragments showed an increase，compared to that under low light.② Under steady-state low O2 the levels of all mRNAs for pigment biosynthetic enzymes declined.

A small and abundant 0.4-kb transcript hybridized with labeled Bam HI-J fragment，which has been mapped to contain crtF and crt E［13，15］［see Figure 3（e）］.Densitometry revealed that the amounts of the 0.4-kb transcript increased about 3-fold when cells were grown under high light relative to that under low light.(https://www.daowen.com)

In addition to the genes for LH-Ⅰ β and a subunits and RC L and M polypeptides，which are clustered in the BamHI-C-EcoRI-B fragment，and the gene for the RC H polypeptide，which is in Bam HI-F fragment of the R'plasmid，DNA sequence data show that the BamHI-C-EcoRI-B fragment contains ORFs C2397 and C2814 and the Bam HI-F fragment contains ORFs F108，F460，F1025，and F1696 and an ORF homologous to the gene for nitrogenase reductase［7，27］.A series of M13 phage DNA probes（see Table 1）specific for those regions was used to determine which regions are transcribed under the described photoheterotrophic or chemoheterotrophic growth conditions.Only a transcript for ORF C2397 was detected by dot blot or electropherogramreplica hybridizations（data not shown）.The mRNA homologous to the gene for C2397 was shown to have the same size（2.6 kb）and same response to light intensity and O2 concentration as the mRNAs for RC-L and RC-M，when a 15-mer oligonucleotide was used as a specific probe（see Table 1）for the gene for C2397（data not shown）.