Genes for LH-I and LH-Ⅱ

A study on absorption spectra of pigments and chromatophores indicated that the synthesis of Bchl is reduced by O2 under steady-state condition and the synthesis of the LH-Ⅱ complex is more strongly repressed by O2 than the LH-Ⅰ complex（data not shown）.This result is supported by measurements of the mRNAs for LH-I and LH-Ⅱ by dot hybridization（see Figure 2，Table 2）.The level of mRNA for LH-Ⅱ was 30 times less in aerobically grown cells as compared to high-light-grown cells.We conclude that the level of mRNA for LH-Ⅱ is more sensitive to O2 concentration than that of the LH-Ⅰ mRNA.This conclusion was further confirmed by blot hybridization of electrophoretically fractionated total RNA.Only one transcript［0.5 kilobase（kb）］for LH-Ⅱ was found［see Figure 3（a）］.Its level was greatly reduced when cells were grown under high O2 conditions.The genes for LH-Ⅰhave two major transcripts：0.5 and 2.6 kb［see Figure 3（b）］.The 0.5-kb transcript is only complementary to the genes for LH-Ⅰβ and α subunits，whereas the 2.6-kb transcript is homologous to the five structural genes coding for LH-I（β，α），RC（L，M）and C2397，as shown by hybridization with specific probes for LH-Ⅰ（see Figure 3（b）），RC-L［see Figure 3（c）］，and RC-M and C2397（data not shown）.The level of the 2.6-kb mRNA appears more sensitive to changes in O2 compared to the 0.5-kb mRNA［see Figure 3（b）and（c）］.(https://www.daowen.com)