Coordination and Interaction of the Genes for LH，R...
The expression of the photosynthetic genes for LH and RC proteins and the accumulation of pigments are tightly coupled and interdependent.Mutation within these genes causes a pleiotropic effect.It has been shown that a mutation in any of the genes for LH-Ⅰ，RC-H，RC-L，Bchl，or Crt biosynthetic enzymes results in different degrees of reduction in the amount of mRNAs from the rest of the genes（O'Brien et al.，unpublished observations；Zhu and Hearst 1987）.O'Brien et al.have used a series of transposon mutants created in this laboratory（Zsebo and Hearst 1984）that carry their defect within or near the structural genes for the RC to study the expression of these genes during photosynthetic development.Insertions within ORF F1696，which is located upstream from the gene for RC-H，caused severe defects in the photosynthetic apparatus.These defects included reduced levels of mRNA for LH-Ⅰ，RC-L，RC-M，and RC-H，along with decreased levels of Bchl mRNA and diminished absorption by LH-Ⅱ.Since we have been unable to detect transcription from the putative F1696 gene（Zhu and Hearst 1986），it seems logical to assume that these insertions blocked the regulatory sequences of the gene for RC-H.Inactivation of the gene for RC-H by an internal mutation resulted in a total loss of LH-Ⅱabsorption and a dramatic decrease in the amount of the RC-L and RC-M proteins as determined by Western blots.Mutations within the gene for the RC-H protein seemed to have a more dramatic effect than those within the gene for the RC-L protein.Such a difference may have resulted from more stringent requirements for the RC-H protein than for the RC-L and RC-M proteins in photosynthetic development（O'Brien et al.，unpublished observations）.On the other hand，mutations in bch（bchC）or crt（crtl）genes substantially reduced levels of mRNA for LH-Ⅱ，LH-Ⅰ，RC-L，RC-M，and RC-H.A close link was found to exist between the genes for LH-Ⅱ proteins and Crt biosynthesis（Zhu and Hearst 1987）.We have also performed experiments to determine whether the decreased levels of mRNA for LH and RC proteins in these mutants are due to reduced transcription or to increased degradation of mRNA.A comparison of the decay rate of mRNAs for LH-Ⅰ，LH-Ⅱ，RC-L，RC-M，and RC-H after treatment with proflavin as an inhibitor of transcription reveals that the mRNAs in the mutants are at least as stable as those in wild-type，although they are present at very low levels.Therefore，the reduction in mRNA levels in these mutants is due to transcriptional control.We suggest that proper and accurate assembly of the photosynthetic components in the ICM is necessary for transcription.Absence of one of these components（either proteins or pigments）may turn off the transcription of the corresponding genes.(https://www.daowen.com)
