A conserved His-Asp signal response regulator-like gene in Heterosigma akashiwo chloroplasts.
Regulation of gene expression in plastids may involve molecular components conserved from cyanobacteria-like ancestors. Among prokaryotes, genes are commonly regulated at the transcriptional level by 'two-component' or 'His-Asp' signal transducers, consisting of a 'sensor kinase', which autophosphorylates at a conserved histidine residue, and a cognate response regulator, which is phosphorylated by the sensor kinase at a conserved aspartate residue. A putative His-Asp response regulator gene (trg1: transcriptional regulatory gene 1) has been identified in the estuarine raphidophytic alga Heterosigma akashiwo. The chloroplast-encoded trg1 is 693 bp in length, contains no introns, and yields a conceptual translation product of 231 amino acids, with a predicted mass of 27 kDa. Homology searches suggest that Heterosigma trgl has an omnpR-like identity within the DNA-binding His-Asp family of response regulators. trg1 contains both the phosphorylation and DNA-binding domains which are present in prokaryote response regulators. Quantitative competitive RT-PCR showed that Heterosigma trg1 is expressed at low levels (5 microg per g total RNA). In contrast, psbA (a photosystem II component) transcript is abundant (60 mg per g total RNA). Cell cycle analysis showed that psbA abundance oscillates in response to light but trg1 mRNA levels are invariant. We hypothesize that a His-Asp phosphorelay mechanism may affect chloroplast genome transcription in a manner similar to bacterial signal transduction pathways in which 'sensor kinase' and cognate 'response regulator' proteins interact.
Jacobs
M A
MA
Department of Botany, University of Washington, Seattle 98195-5325, USA.
Connell
L
L
Cattolico
R A
RA
D020418:Algal Proteins / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D001224:Aspartic Acid / Q000378:metabolism*; D002453:Cell Cycle / Q000235:genetics; D002736:Chloroplasts / Q000235:genetics* / Q000378:metabolism; D017124:Conserved Sequence; D018742:DNA, Chloroplast / Q000737:chemistry / Q000235:genetics; D056890:Eukaryota / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D006639:Histidine / Q000378:metabolism*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D012313:RNA / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
D020418:Algal Proteins; D018742:DNA, Chloroplast; D014157:Transcription Factors; D001224:Aspartic Acid; D006639:Histidine; D012313:RNA