ABSTRACT
Polyamines are organic polycations essential for a wide variety of cellular functions, including nuclear integrity and chromosome condensation. Here we present genetic evidence that depletion of cellular polyamines partially alleviates the defects in HO and SUC2 expression caused by inactivation of the GCN5 histone acetyltransferase. In addition, the combination of polyamine depletion and a sin(-) allele of the histone H4 gene leads to almost complete bypass of the transcriptional requirement for GCN5. In contrast, polyamine depletion does not alter the transcriptional requirements for the SWI/SNF chromatin remodeling complex nor does depletion lead to global defects in transcriptional regulation. In addition to these genetic studies, we show that polyamines facilitate oligomerization of nucleosomal arrays in vitro, and that polyamine-mediated condensation requires intact core histone N-terminal domains and is inhibited by histone hyperacetylation. Our studies suggest that polyamines are repressors of transcription in vivo, and that one role of histone hyperacetylation is to antagonize the ability of polyamines to stabilize highly condensed states of chromosomal fibers.
Subject(s)
DNA-Binding Proteins , Fungal Proteins/metabolism , Histones/metabolism , Polyamines/metabolism , Protein Kinases/metabolism , Saccharomyces cerevisiae Proteins , Acetylation , Fungal Proteins/genetics , Histone Acetyltransferases , Histone Deacetylases/metabolism , Histones/chemistry , Mutation , Nucleosomes/metabolism , Protein Kinases/genetics , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae/metabolism , Spermidine/metabolism , Suppression, Genetic , Transcription, GeneticABSTRACT
The compaction of the eukaryotic genome into a highly folded chromatin structure necessitates cellular mechanisms for allowing access of regulatory proteins to the DNA template. Recent advances in the fields of gene silencing, transcription, recombination, and DNA repair have led to the identification of two distinct families of chromatin remodeling enzymes--nuclear histone acetyltransferases and multisubunit complexes that harbor a SWI2/SNF2 ATPase family member. This paper reviews the current notion of how these enzymes function in remodeling chromatin; we then discuss some tantalizing lines of evidence that lead to the hypothesis that members of both families may actually function in concert to facilitate cellular processes in the context of chromatin.
Subject(s)
Acetyltransferases/physiology , Chromatin/ultrastructure , Chromosomal Proteins, Non-Histone/physiology , Gene Expression Regulation , Multienzyme Complexes/physiology , Nuclear Proteins , Saccharomyces cerevisiae Proteins , Transcription, Genetic/physiology , Acetylation , Adenosine Triphosphatases/genetics , Adenosine Triphosphatases/physiology , Animals , Chromatin/enzymology , Chromatin/physiology , DNA Helicases , DNA-Binding Proteins/genetics , DNA-Binding Proteins/physiology , Fungal Proteins/genetics , Fungal Proteins/physiology , Histone Acetyltransferases , Histones/metabolism , Humans , Macromolecular Substances , Models, Genetic , Multigene Family , Nucleosomes/metabolism , Protein Processing, Post-Translational , Transcription Factors/genetics , Transcription Factors/physiologyABSTRACT
The Saccharomyces cerevisiae SWI/SNF complex is a 2-MDa multimeric assembly that facilitates transcriptional enhancement by antagonizing chromatin-mediated transcriptional repression. We show here that mutations in ADA2, ADA3, and GCN5, which are believed to encode subunits of a nuclear histone acetyltransferase complex, cause phenotypes strikingly similar to that of swi/snf mutants. ADA2, ADA3, and GCN5 are required for full expression of all SWI/SNF-dependent genes tested, including HO, SUC2, INO1, and Ty elements. Furthermore, mutations in the SIN1 gene, which encodes a nonhistone chromatin component, or mutations in histone H3 or H4 partially alleviate the transcriptional defects caused by ada/gcn5 or swi/snf mutations. We also find that ada2 swi1, ada3 swi1, and gcn5 swi1 double mutants are inviable and that mutations in SIN1 allow viability of these double mutants. We have partially purified three chromatographically distinct GCN5-dependent acetyltransferase activities, and we show that these enzymes can acetylate both histones and Sin1p. We propose a model in which the ADA/GCN5 and SWI/SNF complexes facilitate activator function by acting in concert to disrupt or modify chromatin structure.
Subject(s)
Chromatin/genetics , Gene Expression Regulation, Fungal , Saccharomyces cerevisiae Proteins , Saccharomyces cerevisiae/genetics , Transcription, Genetic , Acetylation , Acetyltransferases/metabolism , Chromatin/metabolism , Chromosomal Proteins, Non-Histone/metabolism , Cloning, Molecular , DNA-Binding Proteins/metabolism , Fungal Proteins/metabolism , Genes, Fungal , Histone Acetyltransferases , Protein Binding , Protein Kinases/metabolism , Repressor Proteins/metabolism , Sequence Analysis, DNA , Transcription Factors/metabolismABSTRACT
We report here the isolation of DNA from abdominal tissue of four extinct stingless bees (Proplebeia dominicana) in Dominican amber, PCR amplification of a 546-bp fragment of the 16S rRNA gene from Bacillus spp., and their corresponding nucleotide sequences. These sequences were used in basic local alignment search tool searches of nonredundant nucleic acid data bases, and the highest scores were obtained with 16S rRNA sequences from Bacillus spp. Phylogenetic inference analysis by the maximum-likelihood method revealed close phylogenetic relationships of the four presumed ancient Bacillus sequences with Bacillus pumilus, B. firmus, B. subtilis, and B. circulans. These four extant Bacillus spp. are commonly isolated from abdominal tissue of stingless bees. The close phylogenetic association of the extracted DNA sequences with these bee colonizers suggests that a similar bee-Bacillus association existed in the extinct species P. dominicana.
