Altered expression of nuclear genes encoding chloroplast polypeptides in non-photosynthetic mutants of Chlamydomonas reinhardtii: evidence for post-transcriptional regulation.
In photoautotrophic organisms it is well documented that the expression of nuclear genes encoding plastid proteins can be regulated at various levels. We present here the analysis of a non-photosynthetic strain (CC1051) of the green unicellular alga Chlamydomonas reinhardtii; this strain carries a mutation in the newly identified Cen gene involved in the co-regulated expression of several different nuclear genes encoding plastid proteins. We performed a differential screening strategy to isolate cDNAs corresponding to genes that are differentially expressed in mutant and wild-type strains. Extensive hybridization experiments revealed that the 15 cDNA clones isolated represent five different mRNAs that fail to accumulate in the non-photosynthetic mutant. Comparative analysis of DNA sequencing data showed that they all code for plastid proteins. In particular, we identified genes for the chlorophyll a/b binding protein of the light-harvesting complex II (LHCII), for subunits II and III of photosystem I (PsaD, PsaF), for pentose-5-phosphate 3-epimerase (PPE), an enzyme of the Calvin cycle, and for an unidentified 7 kDa protein with a suggested lumenal location. With the exception of the gene for LHCII, all proteins are encoded by single-copy genes. Evidence from run-on transcription experiments is presented showing that expression of the above mentioned plastid proteins is affected at the post-transcriptional level in the mutant strain CC1051 with a defect in the Cen gene. Our results suggest that the product of the Cen gene is involved in stabilization and/or processing of transcripts from nuclear genes encoding chloroplast proteins.
Hahn
D
D
Lehrstuhl für Allgemeine Botanik, Ruhr-Universität Bochum, Germany.
Bennoun
P
P
Kück
U
U
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016825:Chlamydomonas reinhardtii / Q000235:genetics*; D002736:Chloroplasts / Q000737:chemistry / Q000235:genetics*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics / Q000302:isolation & purification; D005656:Fungal Proteins / Q000235:genetics; D015966:Gene Expression Regulation, Fungal; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics; D010455:Peptides / Q000737:chemistry / Q000235:genetics; D010788:Photosynthesis / Q000235:genetics*; D018087:Plastids / Q000737:chemistry / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic
D018076:DNA, Complementary; D005656:Fungal Proteins; D009687:Nuclear Proteins; D010455:Peptides; D012333:RNA, Messenger