ABSTRACT
lin-4 is essential for the normal temporal control of diverse postembryonic developmental events in C. elegans. lin-4 acts by negatively regulating the level of LIN-14 protein, creating a temporal decrease in LIN-14 protein starting in the first larval stage (L1). We have cloned the C. elegans lin-4 locus by chromosomal walking and transformation rescue. We used the C. elegans clone to isolate the gene from three other Caenorhabditis species; all four Caenorhabditis clones functionally rescue the lin-4 null allele of C. elegans. Comparison of the lin-4 genomic sequence from these four species and site-directed mutagenesis of potential open reading frames indicated that lin-4 does not encode a protein. Two small lin-4 transcripts of approximately 22 and 61 nt were identified in C. elegans and found to contain sequences complementary to a repeated sequence element in the 3' untranslated region (UTR) of lin-14 mRNA, suggesting that lin-4 regulates lin-14 translation via an antisense RNA-RNA interaction.
Subject(s)
Caenorhabditis/genetics , Genes, Helminth , Helminth Proteins/genetics , RNA, Antisense , Animals , Base Sequence , Caenorhabditis/embryology , DNA Primers/chemistry , Gene Expression Regulation , Hydrogen Bonding , Molecular Sequence Data , Nucleic Acid Conformation , Phylogeny , Protein Biosynthesis , RNA, Messenger/genetics , Sequence Alignment , Sequence Homology, Nucleic Acid , Time FactorsABSTRACT
To establish a genetic system for dissection of light-mediated signal transduction in plants, we analyzed the light wavelengths and promoter sequences responsible for the light-induced expression of the Arabidopsis thaliana chalcone synthase (CHS) promoter fused to the beta-glucuronidase (GUS) marker gene. Transgenic A. thaliana lines carrying 1975, 523, 186, and 17 bp of the CHS promoter fused to the GUS gene were generated, and the expression of these chimeric genes was monitored in response to high intensity light in mature plants and to different wavelengths of light in seedlings. Fusion constructs containing 1975 and 523 bp of CHS promoter sequence behaved identically to the endogenous CHS gene under all conditions. Expression of these constructs was induced specifically in response to high intensity white light and blue light. The response to blue light was seen in the presence of the Pfr form of phytochrome. Fusion constructs containing 186 bp of promoter sequence showed reduced basal levels of expression and only weak stimulation by blue light but were induced significantly by high intensity white light. These analyses showed that the expression of the A. thaliana CHS gene is responsive to a specific blue light receptor and that sequences between -523 and -186 bp are required for optimal basal and blue light-induced expression of this gene. The experiments lay the foundation for a simple genetic screen for light response mutants.
Subject(s)
Acyltransferases/genetics , Chimera , Gene Expression Regulation, Enzymologic/radiation effects , Light , Plants/genetics , Blotting, Northern , Glucuronidase/genetics , Phytochrome/metabolism , Plants/enzymology , Promoter Regions, Genetic , RNA, Messenger/analysis , Signal TransductionABSTRACT
We have cloned an Arabidopsis thaliana chalcone synthase (CHS) gene on the basis of cross-hybridization with a Petroselinum hortense CHS cDNA clone. The protein sequence deduced from the A. thaliana CHS DNA sequence is at least 85% homologous to the CHS sequences from P. hortense, Antirrhinum majus, and Petunia hybrida. Southern blot analysis indicated that CHS is a single-copy gene in A. thaliana. High-intensity light treatment of A. thaliana plants for 24 h caused a 50-fold increase in CHS enzyme activity and an accumulation of visibly detectable levels of anthocyanin pigments in the vegetative structures of these plants. A corresponding increase in the steady-state level of CHS mRNA was detected after high-intensity light treatment for the same period of time. The accumulation of CHS mRNA in response to high-intensity light was due, at least in part, to an increased rate of transcription of the CHS gene as demonstrated by nuclear runoff experiments.
Subject(s)
Acyltransferases/genetics , Plant Proteins/genetics , Plants/genetics , Acyltransferases/biosynthesis , Amino Acid Sequence , Base Sequence , DNA/genetics , Enzyme Induction/radiation effects , Light , Molecular Sequence Data , Plant Proteins/biosynthesis , Plants/enzymology , RNA, Messenger/biosynthesis , Transcription, GeneticABSTRACT
The organization of the ribosomal DNA (rDNA) repeat unit in the standard wild-type strain of Neurospora crassa, 74-OR23-1A, and in 30 other wild-type strains and wild-collected strains of N. crassa, . tetrasperma, N. sitophila, N. intermedia, and N. discreta isolated from nature, was investigated by restriction enzyme digestion of genomic DNA, and probing of the Southern-blotted DNA fragments with specific cloned pieces of the rDNA unit from 74-OR23-1A. The size of the rDNA unit in 74-OR23-1A was shown to be 9.20 kilobase pairs (kb) from blotting data, and the average for all strains was 9.11 + 0.21 kb; standard error = 0.038; coefficient of variation (C.V.) = 2.34%. These data indicate that the rDNA repeat unit size has been highly conserved among the Neurospora strains investigated. However, while all strains have a conserved HindIII site near the 5' end of the 25 S rDNA coding sequence, a polymorphism in the number and/or position of HindIII sites in the nontranscribed spacer region was found between strains. The 74-OR23-1A strain has two HindIII sites in the spacer, while others have from 0 to at least 3. This restriction site polymorphism is strain-specific and not species-specific. It was confirmed for some strains by restriction analysis of clones containing most of the rDNA repeat unit. The current restriction map of the 74-OR23-1A rDNA repeat unit is presented.