ABSTRACT
Chloroplast development requires coordinate nuclear and chloroplast gene expression. A putative signal from the chloroplast couples the transcription of certain nuclear genes encoding photosynthesis-related proteins with chloroplast function. We have identified at least three Arabidopsis nuclear genes (GUN1, GUN2, and GUN3) necessary for coupling the expression of some nuclear genes to the functional state of the chloroplast. Homozygous recessive gun mutations allow nuclear gene expression in the absence of chloroplast development and furthermore may interfere with the switch from dark-grown to light-grown development. Other reports suggest this intracellular cross-talk also involves mitochondrial interactions. The GUN genes thus define steps in one specific branch of a complex interorganellar regulatory network.
Subject(s)
Arabidopsis/genetics , Cell Nucleus/metabolism , Chloroplasts/physiology , Genes, Plant , Genes, Regulator , Signal Transduction , Alleles , Arabidopsis/drug effects , Arabidopsis/physiology , Blotting, Northern , Cloning, Molecular , Crosses, Genetic , Ethyl Methanesulfonate/pharmacology , Gene Expression Regulation , Genetic Complementation Test , Homozygote , Mutagenesis , Plants, Genetically Modified , Promoter Regions, Genetic , RNA/genetics , RNA/isolation & purificationABSTRACT
hsp26, the small heat shock protein of Saccharomyces cerevisiae, accumulates in response to heat and other types of stress. It also accumulates during the normal course of development, as cells enter stationary phase growth or begin to sporulate (S. Kurtz, J. Rossi, L. Petko, and S. Lindquist, Science 231:1154-1157, 1986). Analysis of deletion and insertion mutations demonstrated that transcriptional control plays a critical role in regulating HSP26 expression. The HSP26 promoter was found to be complex and appears to contain repressing elements as well as activating elements. Several upstream deletion mutations resulted in strong constitutive expression of HSP26. Furthermore, upstream sequences from the HSP26 gene repressed the constitutive expression of a heterologous heat shock gene. We propose that basal repression and heat-induced depression of transcription play major roles in regulating the expression of HSP26. None of the recombinant constructs that we analyzed separated cis-regulatory sequences responsible for heat shock regulation from those responsible for developmental regulation of HSP26. Depression of HSP26 transcription may be the general mechanism of HSP26 induction in yeast cells. This regulatory scheme is very different from that described for the regulation of most other heat shock genes.
Subject(s)
Genes, Fungal , Heat-Shock Proteins/genetics , Saccharomyces cerevisiae/genetics , Transcription, Genetic , Amino Acid Sequence , Base Sequence , Chromosome Deletion , Gene Expression Regulation, Fungal , Hot Temperature , Molecular Sequence Data , Mutagenesis, Insertional , Oligonucleotide Probes , Restriction Mapping , beta-Galactosidase/genetics , beta-Galactosidase/metabolismABSTRACT
Analysis of the cloned gene confirms that hsp26 of Saccharomyces cerevisiae is a member of the small heat shock protein superfamily. Previous mutational analysis failed to demonstrate any function for the protein. Further experiments presented here demonstrate that hsp26 has no obvious regulatory role and no major effect on thermotolerance. It is possible that the small heat shock protein genes originated as primitive viral or selfish DNA elements.
