Oxygen and Light Regulation of Expression of Genes...
Abstract
The coordinate and differential expression of genes for light harvesting I（LH-Ⅰ）and Ⅱ（LH-Ⅱ）antenna，reaction center（RC）polypeptides L，M，and H，bacteriochlorophyll（Bchl）and carotenoid（Crt）biosynthesis in response to light and O2 in Rhodobacter capsulatus has been studied by measuring the mRNA levels using dot blot and Northern hybridizations.The genes for LH-Ⅱonly have one transcript（0.5 kb），while the genes for LH-Ⅰ have two transcripts（0.5 and 2.6 kb）.The small transcript（0.5 kb）is the mRNA only for LH-Ⅰ（β，α）polypeptides，whereas the large transcript（2.6 kb）codes for RC-L，RC-M，and the β and α polypeptides of LH-Ⅰ，as well as an unknown ORF C2397.These five genes thus comprise a single operon（designated the puf operon）.The mRNA specifying the LH-Ⅱ polypeptides is more abundant，and more sensitive to changes in O2 concentration and shows a variation over a wider range than that of the mRNA for the LH-Ⅰ，indicating that the genes for the LH-Ⅱ and LH-Ⅰ/RC are independently regulated.The gene for RC-H（puh A）has at least two transcripts（1.2 and 1.4 kb）which initiate within ORF F1696 and respond differentially to light intensity.The genes coding for RC-L，RC-M and RC-H are coordinately regulated by light intensity and O2 concentration.We have shown that an increase in light intensity and O2 concentration causes a decrease in the expression of the genes for LH-Ⅰ，LH-Ⅱ，RC proteins，and Bchl biosynthetic enzymes.The genes coding for the enzymes in Crt biosynthetic pathways，however，are regulated in an opposite fashion：high light and high O2 result in increased expression of crt genes.This increased transcription of crt genes is interpreted based on the protective function of Crt against photooxidative damage.An interaction and interdependence of the genes for LH，RC proteins，Bchl and Crt biosynthetic enzymes were also observed using various mutants.
Biggens，J.（ed.），Progress in Photosynthesis Research，Vol.IV.ISBN 90 247 3453 3 © 1987 Martinus Nijhoff Publishers，Dordrecht.Printed in the Netherlands.
此文发表于1987 年“Progress in Photosynthesis Research.”4：717-720.Biggens（ed.）Martinus Nijhoff Publishers，Dordrecht，printed in the Netherland.(https://www.daowen.com)
The purple nonsulfur photosynthetic bacterium，R.capsulatus，provides an attractive model for studying the regulation of photosynthetic genes by light，O2 and other environmental factors.When the concentration of oxygen is lowered，the cell develops an ICM and induces the biosynthesis of LH-Ⅰ（B870），LH-Ⅱ（B800-B850），and RC proteins，as well as Bchl and Crt［13］.Once assembled，the photochemically active complexes harvest and convert light energy into chemical energy.
The genes for theβ（pu f B）and α（puf A）subunits of LH-Ⅰ complex，as well as the L（pufL）and M（pufM）subunits of RC complex，are located in the BamC-EcoB fragment of the R-prime plasmid pRPS404 isolated from R.capsulatus［4］.They are co-transcribed in vivo both in R.capsulatus［5］and Rhodobacter sphaeroides［6，7］.The gene for the H（puhA）subunit of the RC lies in the BamF fragment of the R prime［8］，whereas the genes for the β（pucB）and α（pucA）subunits of the LH-Ⅱ are outside of this photosynthetic gene cluster［9］.The structural genes for LH-Ⅰ，LH-Ⅱ and RC-L，RC-M，RC-H in R.capsulatus have been sequenced［4，8，9］.The genes for Bchl and Crt biosynthesis have been mapped by genetic methods［10］and transposon mutagenesis［11］.
In this paper we report a systematic investigation of mRNAs of photosynthetic genes in R.capsulatus under different growth conditions using dot and Northen hybridizations.The results show a coordinate and differential regulation of the genes for LH（Ⅰ，Ⅱ），RC（L，M，H）and pigment（Bchl，Crt）biosynthesis by light intensity and O2 concentration.
