G1 Gene Research Articles

Disruption of Netrin G1 by a balanced chromosome translocation in a girl with Rett syndrome

We have identified a girl with characteristic features of Rett syndrome (RTT) who carries a de novo balanced translocation involving chromosomes 1 and 7. Both breakpoints were mapped by fluorescence in situ hybridization with selected genomic clones from the regions of interest. Southern blot hybridisations, utilizing probes derived from breakpoint spanning BACs, detected several aberrant fragments specific for the patient. Sequence analysis of the cloned junction fragment indicated that on chromosome 1 the predominantly brain-expressed Netrin G1 (NTNG1) gene is disrupted, whereas on chromosome 7 there was no indication for a truncated gene. The chromosome 1 breakpoint lies within the 3' part of NTNG1 and affects alternatively spliced transcripts, suggesting that the phenotype in this patient is the result of disturbed NTNG1 expression. In silico translation of the NTNG1 splice variants predicted protein isoforms with different C-termini: one membrane bound through a glycosylphosphatidylinositol anchor and the other soluble. The membrane-bound protein isoform would be affected by the breakpoint, whereas the soluble form would remain intact. Our results suggest that the central nervous system is sensitive to NTNG1 expression levels and that NTNG1 is a novel candidate disease gene for RTT.

Analysis of part of M gene and genotyping for M segment of hantavirus detected from HFRS patients' sera in Qingdao region during 2000 - 2003

To study the molecular epidemiological characteristics of hantavirus seen during 2000-2003 in Qingdao region of Shandong province. Sera were collected from 64 patients with hemorrhagic fever with renal syndrome (HFRS) and viral RNA was extracted from the sera. HTN and SEO universal primers were designed as outer primers and HTN and SEO specific primers as inner primers. G1 gene region of M segment from hantavirus was amplified by using RT-nest-PCR for sequencing. The data of nucleotide sequences were analyzed by DNA star software. Six cases were positive by HTN specific primer of total cases (9%); 25 of 64 cases by SEO specific primer (39%); total positive rate was 48%. In general, SEO type was a prevalent type of hantavirus in Qingdao region. The variation of the nucleotide sequences among SEO viruses (nucleotide sequence divergence ranged from 0.3% approximately 8.9%) was lower than that among HTN type (nucleotide sequence divergence ranged from 2.6% approximately 11.2% ). Majority of hantavirus found in Qingdao region belonged to SEO type and still a few strains belonged to HTN type. Most of the HTN viruses were detected in Jiaonan county.

Increased DNA breaks and up-regulation of both G1 and G2 checkpoint genes p21WAF1/CIP1 and 14-3-3 ? in circulating leukocytes of glaucoma patients and vasospastic individuals

Vascular disorder leading to local ischemia/reperfusion has been shown to play an important role in the glaucomatous damage. A decreased expression level of XPGC-gene has been found in circulating leukocytes of normal-tension glaucoma patients. Although decreased activity of XPGC-gene leads to insufficient DNA-repair, no leukopenia has been observed in glaucoma. Molecular mechanisms ensuring cell survival have not been elucidated yet for glaucoma with vascular disorder. Using the ex vivo optical imaging method of alkaline "comet assay" comparative quantification of DNA breaks was performed in circulating leukocytes of non-glaucomatous non-vasospastic and vasospastic individuals as well as both normal-tension and high-tension glaucoma patients. Relative expression levels of the anti-apoptotic factors P21(WAF1/CIP1) and 14-3-3 sigma were investigated in all groups tested. The quantification of P21(WAF1/CIP1) showed the highest expression rates in high-tension glaucoma patients which were significantly higher than those in all other groups tested. The highest expression rates of 14-3-3 sigma were found in both groups of glaucoma patients. These expression levels correlated well with DNA breaks measured. Since the expression of P21(WAF1/CIP1) in leukocytes was shown to be crucial for their survival under stress conditions, we suppose further that the up-regulation of this gene is the key event in the survival mechanisms of leukocytes in glaucoma accompanied with vascular disorder. The p21(WAF1/CIP1) gene should be further taken into consideration as a potential marker, the up-regulation of which in circulating leukocytes of vasospastic individuals may indicate an increased risk for the developing glaucoma.

A family-based association study and gene expression analyses of netrin-G1 and -G2 genes in schizophrenia

The netrin-G1 (NTNG1) and -G2 (NTNG2) genes, recently cloned from mouse, play a role in the formation and/or maintenance of glutamatergic neural circuitry. Accumulating evidence strongly suggests that disturbances of neuronal development and the N-methyl-d-aspartate receptor-mediated signaling system might represent a potential pathophysiology in schizophrenia. We therefore set out to examine the genetic contribution of human NTNG1 and NTNG2 to schizophrenia. Twenty-one single nucleotide polymorphisms (SNPs) from NTNG1 and 10 SNPs from NTNG2 were analyzed in 124 schizophrenic pedigrees. All genotypes were determined with the TaqMan assay. The expression levels of NTNG1 and NTNG2 were examined in the frontal (Brodmann's Area [BA]11 and BA46) and temporal (BA22) cortices from schizophrenic and control postmortem brains. The isoform-specific expression of NTNG1 splice variants was assessed in these samples. Specific haplotypes encompassing alternatively spliced exons of NTNG1 were associated with schizophrenia, and concordantly, messenger ribonucleic acid isoform expression was significantly different between schizophrenic and control brains. An association between NTNG2 and schizophrenia was also observed with SNPs and haplotypes that clustered in the 5' region of the gene. The NTNG1 and NTNG2 genes might be relevant to the pathophysiology of schizophrenia.

Cyclin G1 and Cyclin G2 Are Expressed in the Periimplantation Mouse Uterus in a Cell-Specific and Progesterone-Dependent Manner: Evidence for Aberrant Regulation with Hoxa-10 Deficiency

Because uterine cell-specific proliferation, differentiation, and apoptosis are differentially regulated during the periimplantation period, we speculated that negative cell cycle regulators are also operative in the uterus during this period. This prompted us to examine the roles of two negative growth-regulatory genes, cyclin G1 and cyclin G2, in the periimplantation mouse uterus. We show that cyclin G1 and cyclin G2 genes are differentially regulated in the uterus during this period (d 1-8 of pregnancy) in a spatiotemporal manner. The results suggest that cyclin G1 is primarily associated with epithelial cell differentiation before implantation and stromal cell proliferation and differentiation during decidualization, whereas cyclin G2 is associated with terminal differentiation and apoptosis of the luminal epithelial and stromal cells at the site of blastocyst after implantation. Pharmacological and genetic studies provide evidence that the expression of cyclin G1, not cyclin G2, is regulated by progesterone via its nuclear receptor. Furthermore, the expression of these genes is aberrantly up-regulated in homeo box A-10 mutant uteri, suggesting that cyclin G1 and cyclin G2 genes act as downstream targets of homeobox A-10 and negatively impact uterine cell proliferation. Collectively, our present and previous studies suggest that negative cell cycle regulators collaborate with growth-promoting regulators in regulating uterine cell-specific proliferation, differentiation, and apoptosis relevant to implantation and decidualization.

Combined haploid and insertional mutation screen in the zebrafish

To identify genes required for development of the brain and somites, we performed a pilot screen of gynogenetic haploid zebrafish embryos produced from mothers mutagenized by viral insertion. We describe an efficient method to identify new mutations and the affected gene. In addition, we report the results of a small-scale screen that identified five genes required for brain development, including novel alleles of nagie oko, pou5f1, ribosomal protein L36, and n-cadherin, as well as a novel allele of the laminin g1 gene that is required for normal skeletal muscle fiber organization and somite patterning.

Decreased expression of the candidate tumor suppressor gene ING1 is associated with poor prognosis in advanced neuroblastomas

ING1 has been identified as a novel candidate tumor suppressor gene using a genetic suppressor element (GSE) strategy. Ectopic expression of ING1 in mammalian cultured cells causes cell cycle arrest and apoptosis through a p53-dependent and/or p53-independent pathway. However, there has been no report on the prognostic significance of the ING1 expression level in human cancers, though the expression of the wild-type ING1 gene is significantly decreased in breast, lymphoid and gastric cancers as compared with their corresponding normal tissues. In order to explore the possible involvement of ING1 in tumorigenesis of neuroblastoma, we examined the expression levels of ING1 mRNA in 32 primary neuroblastomas by using a quantitative real-time PCR. ING1 mRNA was expressed independently of the disease stages. however, low levels of ING1 mRNA were significantly associated with a poor prognosis (log-rank test, p=0.017). Multivariate analysis showed that the expression level of ING1 was closely related to survival (p=0.020), even after controlling with age (p=0.008) or stage (p=0.025), while it was only marginally significant after controlling with TrkA expression (p=0.063). Mutation analysis revealed that there was no mutation or deletion of the ING1 gene except 1 silent mutation at codon 188 in primary neuroblastomas examined. Taken together, our results suggest for the first time that a decreased level of ING1 expression is a novel indicator of poor prognosis in advanced stages of neuroblastoma, and that ING1 may play a crucial role in genesis and progression of neuroblastoma.

Expression of main neutralization antigen VP7 of human rotavirus serotype G2 and G3 by recombinant adenoviruses

To express main neutralization antigen VP7 of human rotavirus serotype G2 and G3 by recombinant adenoviruses on the basis of previous investigation of the prevalence of rotavirus in China. On the basis of successfully expression of human rotavirus protein G1VP7 by recombinant adenovirus vector, the authors constructed some potent recombinant adenovirus strains encoding rotavirus G2 VP7 and G3 VP7 genes which belong to the main rotavirus isolates 97S43 and 97S48. Replication defective recombinant adenoviruses expressing human rotavirus serotype G2 and G3 VP7 genes, named as rvAdG2VP7 and rvAdG3VP7 were successfully constructed. VP7 genes integrated into the viral genome were identified by PCR and Southern blot assay, and specific transcription were detected by RT-PCR in the 293 cells infected with recombinant adenoviruses. Expression of rotavirus VP7 proteins was demonstrated by Western blot assay. The established recombinant adenoviruses expressing G2 and G3 serotype VP7s laid a significant basis for further animal experiments in the development of multivalent rotavirus vaccines against rotavirus infection.

840 Quality assurance in conformal prostate radiation therapy: technology questionnaire for EORTC trial 22991

Hypoxia-inducible factors (HIFs) and vascular endothelial growth factor (VEGF) have critical roles during the development of the fetomaternal unit. The HIFs regulate placentation and vascularization by stimulation of VEGF gene expression. This study aimed to investigate the expression profiles of HIF gene family and VEGF in the cat uterus during pregnancy. Tissue samples of the whole uterine wall were collected after ovariohysterectomy and allocated to the following groups: embryo positive (group 1 [G1], n = 7, 7 days after mating), early pregnancy (group 2 [G2], n = 7, 20 days after mating), mid-pregnancy (group 3 [G3], n = 7, 24 days after mating), late pregnancy (group 4 [G4], n = 7, 30–45 days after mating), and oocyte positive groups (group 5 [G5], n = 7, 7 days after induction of ovulation with GnRH analog). Relative mRNA levels were determined by real-time polymerase chain reaction. As housekeeping gene, glyceraldehyde-3-phosphate dehydrogenase was used. The relative gene expression of HIF1A in G5 was found to be significantly higher than that of other groups (G1, G2, G3, and G4) (P < 0.05). In addition, the expression of HIF2A in G5 was higher than that of G1 and HIF2A gene expression at placentation sites of G4 was higher than in G1, G2, and G3 (P < 0.05). Immunohistochemistry indicated that HIF1A, HIF2A, and VEGF expressions were observed in different cell types of uterine and placental tissues in late pregnancy and oocyte groups. The expression of HIF3A did not change significantly in any group investigated. These observations suggest that HIFs and VEGF may play a role in the establishment and development of pregnancy.

Mechanisms of benzene-induced hematotoxicity and leukemogenicity: cDNA microarray analyses using mouse bone marrow tissue.

Although the mechanisms underlying benzene-induced toxicity and leukemogenicity are not yet fully understood, they are likely to be complicated by various pathways, including those of metabolism, growth factor regulation, oxidative stress, DNA damage, cell cycle regulation, and programmed cell death. With this as a background, we performed cDNA microarray analyses on mouse bone marrow tissue during and after a 2-week benzene exposure by inhalation. Our goal was to clarify the mechanisms underlying the hematotoxicity and leukemogenicity induced by benzene at the level of altered multigene expression. Because a few researchers have postulated that the cell cycle regulation mediated by p53 is a critical event for benzene-induced hematotoxicity, the present study was carried out using p53-knockout (KO) mice and C57BL/6 mice. On the basis of the results of large-scale gene expression studies, we conclude the following: (a) Benzene induces DNA damage in cells at any phase of the cell cycle through myeloperoxidase and in the redox cycle, resulting in p53 expression through Raf-1 and cyclin D-interacting myb-like protein 1. (b) For G1/S cell cycle arrest, the p53-mediated pathway through p21 is involved, as well as the pRb gene-mediated pathway. (c) Alteration of cyclin G1 and Wee-1 kinase genes may be related to the G2/M arrest induced by benzene exposure. (d) DNA repair genes such as Rad50 and Rad51 are markedly downregulated in p53-KO mice. (e) p53-mediated caspase 11 activation, aside from p53-mediated Bax gene induction, may be an important pathway for cellular apoptosis after benzene exposure. Our results strongly suggest that the dysfunction of the p53 gene, possibly caused by strong and repeated genetic and epigenetic effects of benzene on candidate leukemia cells, may induce fatal problems such as those of cell cycle checkpoint, apoptosis, and the DNA repair system, finally resulting in hemopoietic malignancies. Our cDNA microarray data provide valuable information for future investigations of the mechanisms underlying the toxicity and leukemogenicity of benzene.

A Seed-specific Heat-shock Transcription Factor Involved in Developmental Regulation during Embryogenesis in Sunflower

We report the cloning and functional characterization of the first heat-shock transcription factor that is specifically expressed during embryogenesis in the absence of environmental stress. In sunflower embryos this factor, HaHSFA9, trans-activated promoters with poor consensus heat-shock cis-elements, including that of the seed-specific Hahsp17.6G1 gene. Mutations that improved the heat-shock cis-element consensus at the Hahsp17.7G4 promoter impaired transient activation by HaHSFA9 in sunflower embryos. The same mutations did not affect heat-shock-induced gene expression of this promoter in transgenic tobacco plants but reduced the developmental activation by endogenous heat-shock transcription factors (HSFs) in seeds. Sunflower, and perhaps other plants such as tobacco, differs from the vertebrate animal systems in having at least one specialized HSF with expression and (or) activation patterns strictly restricted to embryos. Our results strongly indicate that HaHSFA9 is a transcription factor critically involved in the developmental activation of Hahsp17.6G1 and in that of similar target genes as Hahsp17.7G4.

Cyclin G1 is involved in G2/M arrest in response to DNA damage and in growth control after damage recovery.

Cyclin G1 is one of the target genes of the transcription factor p53, and is induced in a p53-dependent manner in response to DNA damage. Although cyclin G1 has been implicated in a range of biological phenomena, its precise function remains unclear. Here we present an analysis of the physiological role of cyclin G1 using mice homozygous for a targeted disruption of the cyclin G1 gene. In order to clarify the role of cyclin G1 in the p53 pathway, downstream events such as apoptosis, cell growth and cell cycle checkpoint control were analysed in thymocytes and embryonic fibroblasts derived from cyclin G1-disrupted mice. No difference was detected in induction of apoptosis between mouse embryo fibroblasts (MEFs) derived from cyclin G1+/+ and cyclin G1-/- mice. Following irradiation, cyclin G1-/- MEFs proliferated more slowly and reached lower cell densities in culture dishes than cyclin G1+/+ MEFs. Analysis of cell survival showed that cyclin G1-/- MEFs were about twice as sensitive as cyclin G1+/+ MEFs to gamma radiation or UV radiation. Cyclin G1-/- mice were more sensitive to gamma radiation than wild-type mice. Flow cytometeric analysis revealed that the number of cyclin G1-/- MEFs in G2/M phase after irradiation was reduced by 50% relative to cyclin G1+/+ MEFs. Our results demonstrate that cyclin G1 plays roles in G2/M arrest, damage recovery and growth promotion after cellular stress.

Mutational analysis of the candidate tumor suppressor gene ING1 in Indian oral squamous cell carcinoma.

ING1, a recently identified candidate tumor suppressor gene, involved in the p53 signaling pathway is mapped at chromosome 13q34. Since loss of heterozygosity at 13q34 has been reported in squamous cell carcinoma of head and neck, we screened for mutations in ING1 by polymerase chain reaction-single strand conformation polymorphism in 71 oral squamous cell carcinomas (OSCC) from India, 15 of which were known to harbor p53 mutations. A single polymorphism (G to A) was detected in 14 (19.7%) of the tumors analyzed. No mutation was observed in any of the 71 OSCCs analyzed. These results suggest that ING1 is not a target for mutational inactivation in OSCC of Indians.

Genomic structure, alternative splicing, and physical mapping of the killer cell lectin-like receptor G1 gene (KLRG1), the mouse homologue of MAFA.

The mouse killer cell lectin-like receptor G1 (KLRG1), the mouse homologue of the mast cell function-associated antigen (MAFA), is an inhibitory C-type lectin expressed on natural killer (NK) cells and activated CD8 T cells. Here we report the complete nucleotide sequence, alternatively spliced variants, and the physical mapping of the KLRG1 gene in the mouse. The gene spans about 13 kb and consists of five exons. Short interspersed repeats of the B1 and B2 family, a LINE-1-like element, and a (CTT)170 triplet repeat were found in intron sequences. In contrast to human KLRG1 and to the murine KLR family members, mouse KLRG1 locates outside the NK complex on Chromosome 6 between the genes encoding CD9 and CD4.

Allele polymorphism of a new pentanucleotide STR marker located to an intron of the tumor suppressor gene ING1

Using polymerase chain reaction (PCR) DNA samples of unrelated subjects from the Volga-Ural region of Russia were examined to study allele polymorphism of the pentanucleotide repeat (TTGTG) g localized to an intron of the tumor suppressor gene ING1. STR marker was registered in the EMBL database with the accession number AJ277387. In a sample of 119 individuals, three pentanucleotide alleles consisting of seven, eight, and nine repeated monomers were revealed. The allele frequencies were 0.24, 0.74, and 0.02, respectively. Heterozygosity was 0.45. On the basis of these data, the repeat can be regarded as a polymorphic STR marker for the ING1 gene and used in population and clinical studies.

In vivo expression and genomic organization of the mouse cyclin I gene ( Ccni)

Cyclins control cell-cycle progression by regulating the activity of cyclin-dependent kinases. Cyclin I was recently added to the cyclin family of proteins because of the presence of a cyclin box motif in the deduced amino-acid sequence. Cyclin I may share functional roles with cyclin G1 and G2 because of the high structural similarity between their deduced amino-acid sequences. However, the biological and functional roles of this subclass of cyclins remain obscure. The mouse cyclin G1 and G2 genes have previously been cloned and characterized. In this report, we describe the cloning of the mouse homolog of cyclin I. The cyclin I cDNA sequence was used to determine the genomic organization of the mouse cyclin I gene which co-localizes with cyclin G2 to chromosome 5E3.3–F1.3. Cyclin I was transcribed from seven exons distributed over more than 19 kb of genomic sequence. The expression of cyclin I was determined in various tissues, but no clear correlation with the proliferative state was found. Furthermore, in contrast to cyclin G1, cyclin I expression was stable during cell-cycle progression after partial hepatectomy in both the absence and presence of DNA damage. Transient expression of cyclin I–green fluorescent protein (GFP) fusion proteins in cell lines showed that cyclin I was distributed throughout the cell in contrast with the mainly cytoplasmic localization of cyclin G2 and nuclear localization of cyclin G1. Our results indicate that despite the close structural similarity between cyclin G1, G2 and I, these three proteins are likely to have distinct biological roles.

Identification and localization of conserved antigenic epitopes on the G2 proteins of California serogroup Bunyaviruses.

California (CAL) serogroup Bunyaviruses are significant agents of arboviral encephalitis in humans. They are maintained and transmitted in nature by mosquitoes to preferred vertebrate amplifying hosts. The G2 envelope glycoprotein of La Crosse virus (LAC) was proposed by Ludwig et al. to be a determinant for virus attachment to mosquito midgut cells. Monoclonal antibodies to G2 neutralize the infectivity of pronase-treated virus for mosquito cells. We determined the location of antigenic sites on the LAC G2. We showed that antigenic areas present on the LAC G2 protein are conserved among viruses in the California encephalitis and Melao subgroups of the CAL serogroup, but not in trivatattus virus, nor within the BUN serogroup. A comparison of the G2 exodomain amino acid sequences of eight CAL and three BUN viruses with monoclonal antibodies (MAb) binding data predicted the possible location of the antigenic sites. We used in vitro mutagenesis of the LAC G2 gene to construct a set of G2 genes with replacement sequences in the coding regions for the suspected MAb binding sites. The native and mutated proteins were expressed in Hela cells and the ability of MAbs to bind to the expressed proteins was tested. Four discontinuous amino acid sequences, conserved among eight CAL serogroup viruses, were identified as contributing to two conformational binding domains for neutralizing LAC G2 MAbs.

Molecular analysis of the candidate tumor suppressor gene ING1 in human head and neck tumors with 13q deletions.

The candidate tumor-suppressor gene ING1 encodes p33(ING1), a nuclear protein which physically interacts with TP53. It has been shown that p33(ING1) acts in the same biochemical pathway as TP53, leading to cell growth inhibition. Interestingly, a rearrangement of the ING1 gene was found in a neuroblastoma cell line, supporting its involvement in tumor development. Because ING1 resides on the long arm of chromosome 13 (13q34) (a region frequently deleted in many tumor types), we sought to characterize its role in head and neck squamous-cell carcinoma (HNSCC). We first analyzed 44 primary tumors for loss of heterozygosity (LOH) at 13q, using four widely spaced microsatellite markers (13q14, 13q14.3-q22, 13q22, and 13q34). Twenty (48%) of the tumor samples showed LOH in all of the informative markers tested, including D13S1315 at 13q34. Two of the tumors displayed partial losses restricted to one marker (D13S118 at 13q14 in tumor 1164, and D13S135 at 13q14.3-q22 in tumor 1398). We then determined the genomic structure of the ING1 gene and sequenced the entire coding region in 20 primary tumors showing 13q LOH and in five head and neck cancer cell lines. A single germline polymorphism was detected in 10 of the tumors analyzed (T to C change) located 110 nucleotides upstream of the starting methionine. No somatic mutations were found in any of the samples, suggesting that ING1 is not a tumor suppressor gene target in head and neck cancer. Genes Chromosomes Cancer 27:319-322, 2000.

Inhibition of rabbit keratocyte and human fetal lens epithelial cell proliferation by retrovirus-mediated transfer of antisense cyclin G1 and antisense MAT1 constructs.

The aim of this study is to evaluate the potential of gene transfer of cell cycle control genes as treatment of corneal haze or secondary cataract formation. The guiding hypothesis is that strategic modulation of the cyclin G1 or MAT1 gene by retrovirus-mediated gene transfer will inhibit proliferation of rabbit keratocytes (RabK) and fetal human lens epithelial (FHLEpi) cells in vitro. RabK and FHLEpi cell cultures were transduced in triplicate with retroviral vectors bearing either a nuclear-targeted beta-galactosidase, an antisense cyclin G1 (aG1), an antisense MAT1 (aMAT1) construct, or the neo(r) gene. The presence of beta-galactosidase activity in the transduced cultures was detected by immunohistochemical X-Gal staining, while cyclin G1 and MAT1 protein expression levels were evaluated by Western analysis. Proliferation of RabKs and FHLEpi cells was analyzed by counting the number of cells in the aG1 and aMAT1 vector-transduced cultures over 5 days. The mean transduction efficiency was 34.4% (SD 1.41) for RabKs and 19.7% (SD 1.83) for FHLEpi cells. Downregulation of cyclin G1 and MAT1 protein expression was noted 24 hr after transduction of RabK cultures with the respective vectors. Cytostatic effects of the aG1 and aMAT1 vectors in both RabKs and FHLEpi cells were most pronounced on the fifth day (RabKs, p < 0.0007; FHEpi cells, p < 0.001). An increased incidence of apoptosis was identified in both aG1 and MAT1-transduced FHLEpi cells. Taken together, these data suggest the potential utility of developing aG1 and aMAT1 retroviral vectors in gene therapy protocols for corneal haze and secondary cataract formation.

Cell cycle-regulated histone acetylation required for expression of the yeast HO gene.

Expression of the yeast HO gene in late G1 of the cell cycle requires the SWI/SNF chromatin remodeling complex, the Gcn5p histone acetyltransferase, and two different sequence-specific transcriptional activators, Swi5p and Swi4p/Swi6p. We have used chromatin immunoprecipitation assays to investigate the role of each of these trans-acting factors in establishing a cell cycle-regulated domain of histone acetylation surrounding the HO upstream regulatory region. We detect a approximately 1-kb domain of H3 and H4 acetylation that is established in mid-G1, prior to and independent of HO transcription, which then declines with kinetics similar to inactivation of HO. This cell cycle burst of histone acetylation requires Gcn5p, SWI/SNF, and the Swi5p activator, but occurs in the absence of the Swi4p activator. We also find that inactivation of the Sin3p/Rpd3p deacetylase complex leads to a high level of acetylation at the HO locus throughout the cell cycle. We propose a sequential model for activation of HO in which the Swi5p-dependent recruitment of the Gcn5p acetyltransferase requires chromatin remodeling events by the SWI/SNF complex.