Promoter Histone H3 Research Articles

Tissue-dependent enhancement of transgene expression by introns of replacement histone H3 genes of Arabidopsis.

Intron-bearing replacement histone H3 genes in Arabidopsis and other plants are highly and constitutively expressed. We demonstrate that the introns located within the 5'-untranslated regions (5'-UTR) of the two Arabidopsis replacement H3 genes will abolish the cell cycle dependence of an endogenous histone H4 promoter. We demonstrate that these introns, functionally combined with their endogenous promoters, could produce the high and constitutive expression of the replacement H3 genes observed in planta. They strongly increase gene expression whatever the promoter, from the strong 35S CaMV promoter to complete and resected promoters of cell cycle-dependent and replacement histone genes. Quantitative analysis of the extent of reporter gene enhancement in different parts of developing transgenic plantlets, ranging from 2-fold to 70-fold, supports the notion that trans-acting factors are responsible for this effect. Such factors appear most abundant in roots.

Isolation and use of a homologous histone H4 promoter and a ribosomal DNA region in a transformation vector for the oil-producing fungus Mortierella alpina.

Mortierella alpina was transformed successfully to hygromycin B resistance by using a homologous histone H4 promoter to drive gene expression and a homologous ribosomal DNA region to promote chromosomal integration. This is the first description of transformation in this commercially important oleaginous organism. Two pairs of histone H3 and H4 genes were isolated from this fungus. Each pair consisted of one histone H3 gene and one histone H4 gene, transcribed divergently from an intergenic promoter region. The pairs of encoded histone H3 or H4 proteins were identical in amino acid sequence. At the DNA level, each histone H3 or H4 open reading frame showed 97 to 99% identity to its counterpart but the noncoding regions had little sequence identity. Unlike the histone genes from other filamentous fungi, all four M. alpina genes lacked introns. During normal vegetative growth, transcripts from the two histone H4 genes were produced at approximately the same level, indicating that either histone H4 promoter could be used in transformation vectors. The generation of stable, hygromycin B-resistant transformants required the incorporation of a homologous ribosomal DNA region into the transformation vector to promote chromosomal integration.

S phase-specific DNA-binding proteins interacting with the Hex and Oct motifs in type I element of the wheat histone H3 promoter.

The type I element (CCACGTCANCGATCCGCG), consisting of the Hex motif (CCACGTCA) and the reverse-oriented Oct motif (GATCCGCG), is necessary and sufficient to confer the S phase-specific transcription of the wheat histone H3 (TH012) gene. The transcriptional regulation via the type I element is thought to occur through interactions between transcription factors which bind specifically to the Hex and Oct motifs. Here we report S phase-specific DNA-binding proteins interacting with the type I element in partially synchronized wheat cultured cells. Hex motif-binding proteins found here resembled HBP-1a, as reported previously in terms of DNA-binding specificity. DNA-binding activities of the HBP-1a-like proteins were modulated by phosphorylation/dephosphorylation. In the electrophoretic mobility shift assay of the wheat nuclear extract, we also found three Oct motif-specific binding proteins, named OBRF (octamer-binding regulatory factor)-1, -2 and -3. One of the HBP-1a-like proteins and OBRF-1 appeared predominantly at the S phase. Thus, it was supposed that these two factors play a crucial role in the S phase-specific regulation of wheat histone gene expression.

Meristem, cell division and S phase-dependent activity of wheat histone H4 promoter in transgenic maize plants

We have studied the activity of a wheat histone H4 promoter in transgenic maize plants produced by direct DNA uptake into embryogenic cell suspension protoplasts. Expression patterns revealed by fluorimetric as well as histochemical GUS reporter enzyme assays and Northern hybridisation indicated the cell division-dependent expression of the GUS gene driven by the histone H4 promoter in proliferating cells and meristems. Changes in gene expression associated with the progression through the cell cycle in maize cell-suspension cultures were also investigated after partial synchronisation of cell division by aphidicolin or hydroxyurea. The transgene expression regulated by the wheat histone H4 promoter coincided with elevated levels of mRNAs from other S phase-associated genes such as maize histone H4, histone H2B and proliferating cell nuclear antigen ( PCNA) . The reporter gene expression was low during mitosis when accumulation of the transcripts of a B-type mitotic cyclin CycB1;zm;1 could be detected. The presented data indicate that the used 720-bp-long promoter region can provide replication-dependent expression for the GUS reporter gene in transgenic maize. In these maize plants, external hormone stimuli generated by a synthetic auxin 2,4-dichlorophenoxy acetic acid (2,4-D) or abscisic acid (ABA) have modified the histone H4 promoter-driven GUS gene transcription. These findings support the usefulness of the H4::GUS transgenic plants for further studies on cell cycle activation/inactivation by mitogenic or stress related stimuli in maize.

Follicle-stimulating hormone promotes histone H3 phosphorylation on serine-10.

FSH promoted the rapid phosphorylation of the nuclear protein histone H3 in immature rat ovarian granulosa cells under experimental conditions that lead to cellular differentiation and not proliferation. FSH-stimulated histone H3 phosphorylation correlated with cAMP-dependent protein kinase A (PKA) activation and translocation of the PKA catalytic subunit to a nuclear-enriched fraction and was inhibited by the PKA inhibitor H89, and histone H3 phosphorylation was stimulated in cells treated with agents that raise intracellular cAMP levels such as forskolin and 8-bromo-cAMP. FSH-stimulated histone H3 phosphorylation in granulosa cells mapped to ser-10, a site previously identified as the PKA phosphorylation site in various mitotically active cells as the mitosis-specific phosphorylation site. Injection of the FSH analog PMSG to immature rats, which is known to stimulate granulosa cell proliferation as well as differentiation, also promoted histone H3 phosphorylation on ser-10 in granulosa cells. These results establish that FSH-stimulated histone H3 phosphorylation in granulosa cells is linked not only to granulosa cell mitosis but also to granulosa cell differentiation and that FSH-stimulated histone H3 phosphorylation on ser-10 in isolated granulosa cells is mediated by PKA. These results also identify the PKA-dependent histone H3 phosphorylation as an early nuclear protein marker for FSH-stimulated differentiation of granulosa cells. Based on the recently described function of histone H3 as a coactivator of transcription, these results are consistent with the hypothesis that phosphorylated histone H3 may facilitate PKA-dependent gene transcription in granulosa cells leading to the preovulatory phenotype.

Cooperation of two distinct cis‐acting elements is necessary for the S phase‐specific activation of the wheat histone H3 promoter

We have previously shown that the proximal promoter region (−185 to +57) of the wheat histone H3 gene (TH012) is sufficient for regulating S phase‐specific expression of a reporter GUS gene. To define the cis‐acting element(s) responsible for S phase‐specific expression, GUS fusion genes under the control of wild‐type or variously mutated H3 promoters were stably introduced into cultured rice Oc cells and their temporal expression was analyzed during the cell cycle by quantitative S1 analysis. The S phase‐specific expression of the full‐sized promoter (−1716 to +52) was significantly impaired by short internal deletions disrupting the type I element from −175 to −158 (CCACGTCACCaATCCGCG), composed of the Hex (CCACG‐TCA) and reverse‐oriented Oct (GATCCGCG) motifs. Moreover, the H3 proximal promoters (−184 to +52) harboring base‐substitution mutations in either or both of the Hex and Oct motifs could no longer activate gene expression during the S phase. These results indicate that the type I element is the first cis‐acting element identified responsible for the S phase‐specific expression of plant histone genes. Results also suggested the presence of a redundant cis‐acting element(s) responsible for S phase‐specific expression in the H3 far‐upstream region (−1716 to −185).

Analyses of promoter-proximal pausing by RNA polymerase II on the hsp70 heat shock gene promoter in a Drosophila nuclear extract.

Analyses of Drosophila cells have revealed that RNA polymerase II is paused in a region 20 to 40 nucleotides downstream from the transcription start site of the hsp70 heat shock gene when the gene is not transcriptionally active. We have developed a cell-free system that reconstitutes this promoter-proximal pausing. The paused polymerase has been detected by monitoring the hyperreactivity of thymines in the transcription bubble toward potassium permanganate. The pattern of permanganate reactivity for the hsp70 promoter in the reconstituted system matches the pattern found on the promoter after it has been introduced back into files by P-element-mediated transposition. Matching patterns of permanganate reactivity are also observed for a non-heat shock promoter, the histone H3 promoter. Further analysis of the hsp70 promoter in the reconstituted system reveals that pausing does not depend on sequence-specific interactions located immediately downstream from the pause site. Sequences upstream from the TATA box influence the recruitment of polymerase rather than the efficiency of pausing. Kinetic analysis indicates that the polymerase rapidly enters the paused state and remains stably in this state for at least 25 min. Further analysis shows that the paused polymerase will initially resume elongation when Sarkosyl is added but loses this capacity within minutes of pausing. Using an alpha-amanitin-resistant polymerase, we provide evidence that promoter-proximal pausing does not require the carboxy-terminal domain of the polymerase.

Identification of cis-elements regulating the expression of an Arabidopsis histone H4 gene.

Protein-DNA interactions in the proximal region of an Arabidopsis H4 histone gene promoter were analyzed by DMS in vivo footprinting combined with LMPCR amplification. Interactions were identified over six particular sequence motifs, five of which were previously shown to bind proteins in maize histone H3 and H4 promoters and are commonly found in the corresponding regions of other plant histone gene promoters. These motifs are located within a 126 bp fragment which was previously shown to confer preferential expression in meristems of transgenic plants. The contribution of each cis-element to the overall expression level and specificity was investigated by testing individual or combined mutations in transgenic Arabidopsis plants. All five motifs behaved as positive cis-elements of unequal strength. The GCCAAT-like sequence GCCACT behaved as a strong positive cis-element but had no influence on the specificity. In contrast, the nonamer AGATCGACG and to a lesser extent the closely linked hexamer CCGTCG proved to be essential for meristem-specific expression. Involvement of the highly conserved histone-specific octamer CGCGGATC in specific expression was revealed at some stages of meristem development. Importance of these three cis-elements, nonamer, hexamer, and octamer, was further confirmed by the fact that combining mutations of two of them either abolished the promoter activity or completely modified the promoter specificity. Mutation of the fifth cis-element, a degenerate copy of the octamer, little perturbed the promoter function. However disruption of both octamers had a dramatic negative effect, thus suggesting that the two copies cooperate to achieve maximal function in the wild-type promoter, possibly by mobilizing the proliferation-specific factors binding to the nonamer and CCGTCG cis-elements.

Sp1 trans-activation of cell cycle regulated promoters is selectively repressed by Sp3.

The transcription factor Sp1 plays a key role in the activation of many cellular and viral gene promoters, including those that are regulated during the cell cycle. However, recent evidence indicates that Sp1 belongs to a larger family of factors which bind G/C box elements in order to either activate or repress transcription. Sp3, a member of this family, functions to repress transcriptional activation in two viral promoters, most likely by competing with Sp1 for GC box/Sp binding sites. However, the physiological role of Sp3 in the repression of endogenous cellular promoters has not been experimentally addressed. In the present study, we analyze the activity and binding of Sp3 on several eukaryotic promoters that contain G/C boxes and are known to be regulated during cellular proliferation and the cell cycle. Using antibodies specific for Sp1 and Sp3, we observe that both of these factors localize to the cell nucleus and have a similar, dispersed subnuclear distribution. Further, using gel mobility shift assays, we show that both Sp1 and Sp3 interact specifically with the histone H4 promoter. Transient cotransfections of Drosophila cells with Sp1 and Sp3 expression vectors and with the histone H4, thymidine kinase (TK), or dihydrofolate reductase (DHFR) promoters show that only the DHFR promoter, containing multiple functional GC boxes, displays Sp3 repression of Sp1 activation. In contrast, the single G/C boxes within the histone H4 or TK promoters, which confer transcriptional activation via Sp1 binding, are not responsive to repression by Sp3. Therefore, we demonstrate that the endogenous cellular DHFR promoter is selectively responsive to Sp3 repression. The data suggest that Sp3 may contribute to the control of proliferation- and/or cell-regulated promoters depending upon the context and/or number of functional Sp1 binding sites.

Cytokine induction of proliferation and expression of CDC2 and cyclin A in FDC-P1 myeloid hematopoietic progenitor cells: regulation of ubiquitous and cell cycle-dependent histone gene transcription factors.

To evaluate transcriptional mechanisms during cytokine induction of myeloid progenitor cell proliferation, we examined the expression and activity of transcription factors that control cell cycle-dependent histone genes in interleukin-3 (IL-3)-dependent FDC-P1 cells. Histone genes are transcriptionally upregulated in response to a series of cellular regulatory signals that mediate competency for cell cycle progression of the G1/S-phase transition. We therefore focused on factors that are functionally related to activity of the principal cell cycle regulatory element of the histone H4 promoter: CDC2, cyclin A, as well as RB- and IRF-related proteins. Comparisons were made with activities of ubiquitous transcription factors that influence a broad spectrum of promoters independent of proliferation or expression of tissue-specific phenotypic properties. Northern blot analysis indicates that cellular levels of cyclin A and CDC2 mRNAs increase when DNA synthesis and H4 gene expression are initiated, supporting involvement in cell cycle progression. Using gel-shift assays, incorporating factor-specific antibody and oligonucleotide competition controls, we define three sequential period following cytokine stimulation of FDC-P1 cells when selective upregulation of a subset of transcription factors is observed. In the initial period, the levels of SP1 and HiNF-P are moderately elevated; ATF, AP-1, and HiNF-M/IRF-2 are maximal during the second period; while E2F and HiNF-D, which contain cyclin A as a component, predominate during the third period, coinciding with maximal H4 gene expression and DNA synthesis. Differential regulation of H4 gene transcription factors following growth stimulation is consistent with a principal role of histone gene promoter elements in integrating cues from multiple signaling pathways that control cell cycle induction and progression. Regulation of transcription factors controlling histone gene promoter activity within the context of a staged cascade of responsiveness to cyclins and other physiological mediators of proliferation in FDC-P1 cells provides a paradigm for experimentally addressing interdependent cell cycle and cell growth parameters that are operative in hematopoietic stem cells.

A Far-Upstream Sequence of the Wheat Histone H3 Promoter Functions Differently in Rice and Tobacco Cultured Cells

The cis-regulatory function of a far-upstream sequence (-1,711 to -186) of the promoter of the wheat gene for histone H3 (TH012) was analyzed in cultured rice and tobacco cells in a transient expression system with the gene for beta-D-glucuronidase as a reporter gene. The far-upstream sequence was necessary for full activity of the H3 promoter in rice cells but did not enhance the activity of the proximal promoter in tobacco cells. Dissection analysis of the far-upstream sequence revealed the existence of several positive and negative cis-acting sequences in this region, some of which functioned differently in rice and tobacco cells. In gain-of-function experiments with rice cells, the sequence from -848 to -704, containing the CCAAT and octamer (CaCGGATC) motifs, functioned in an orientation-independent manner, whereas the sequence from -703 to -486 functioned in an orientation-dependent manner. By contrast, both sequences exhibited an orientation-dependent cis-function in tobacco cells. These findings suggest that some cis-regulatory sequences in the far-upstream region of the H3 promoter function differently in rice and tobacco cells.

Trans-activation of the wheat histone H3 promoter by Ga14 DNA-binding domain (1–94) in plant cells

This is the first demonstration that Ga14 DNA-binding domain (1–94) itself has the ability to trans-activate an eukaryotic promoter in vivo. It significantly activated a wheat histone H3 core promoter, but slightly activated a CaMV 35S core promoter in transiently transfected tobacco cells when the Ga14-recognition sequences were put upstream of the core promoters.

Functional Role for Sp1 in the Transcriptional Amplification of a Cell Cycle Regulated Histone H4 Gene

The promoter of the cell cycle regulated histone FO108 H4 gene is mediated by two in vivo protein/DNA interaction domains, sites I and II. We have shown previously that site II mediates the cell cycle controlled enhancement of H4 gene transcription at the G1/S phase boundary. Here we show that site I, an element containing both G-rich and ATF-like consensus sequences, confers maximal levels of transcription in proliferating cells. By the combined application of gel shift assays with site-directed mutagenesis, DNase I footprinting, oligonucleotide competition, in vitro expression of recombinant proteins, and specific antibody supershift studies, we demonstrate that the proximal G-rich sequence within site I interacts with the transcription factor Sp1, while the distal portion of site I interacts with members of the ATF family of proteins, including ATF-1. In vitro transcription studies as well as expression assays of transiently and stably transfected genes in HeLa cells reveal that the deletion of site I causes a dramatic decrease in expression. Mutation of the Sp1 element, which abolishes Sp1 binding, results in a 6-10-fold reduction in reporter activity. In addition, overexpression of Sp1 in Sp1-deficient cells results in the dramatic activation of the histone promoter. In contrast, mutation of the asymmetric ATF binding site, located distally within site I, has a more limited effect upon expression. Interestingly, the contribution of the Sp1 site to maximal transcription was cell type dependent. Thus, we demonstrate that the Sp1 binding site of the site I histone H4 promoter in particular is critical for maximal expression in living cells and postulate that this site may act to amplify the cell cycle response.

Histone H4 proximal promoter mediates a complex transcriptional response during differentiation of 3T3L1 adipocytes

We have investigated the promoter element(s) required by the cell cycle regulated FO108 human histone H4 gene for control of gene expression during adipocyte proliferation and differentiation. Stable 3T3L1 cell lines were established that express fusion genes in which the histone H4 promoter is joined to chloramphenicol acetyltransferase (cat) as a reporter gene. Expression of the H4CAT fusion genes was monitored in proliferating and confluent 3T3L1 preadipocytes and in differentiating 3T3L1 adipocytes. The results indicate that the H4 cell cycle element (CCE), which mediates S phase-specific stimulation of H4 gene transcription, is not required for transcriptional regulation during differentiation. Instead, a minimal H4 promoter (nucleotides -46 to -11) is sufficient to mediate the complex transcriptional response of H4 gene expression observed during the process of adipocyte differentiation of 3T3L1 cells. In addition, the data suggest that down-regulation of histone gene expression during cellular differentiation may be mediated by passive inactivation of the promoter due to loss of positive regulatory factor(s).

Transcription of histone H4, H3, and H1 cell cycle genes: promoter factor HiNF-D contains CDC2, cyclin A, and an RB-related protein.

Cell cycle-controlled human histone genes are coordinately expressed during S phase, and transcriptional regulation involves a series of trans-acting factors (HiNFs). The proliferation-specific factor HiNF-D interacts with multiple recognition motifs in histone H4, H3, and H1 promoters. Using gel shift immunoassays, we show that CDC2, cyclin A, and an RB-related protein are ubiquitous subunits of HiNF-D binding activity isolated from several cell types. HiNF-D levels in vivo are sensitive to okadaic acid and staurosporine, indicating that HiNF-D activity and/or assembly is influenced by phosphorylation status. Thus, HiNF-D appears to be a multicomponent phosphoprotein that participates in coordinate control of multiple histone H4, H3, and H1 genes during the cell cycle. The presence of cell cycle mediators in the HiNF-D complex suggests linkage between transcriptional control of histones, enzymes involved in DNA synthesis, and the onset of DNA replication during the G1/S phase transition.

A histone H4 promoter for expression of a phleomycin-resistance gene in Phanerochaete chrysosporium

In this study, two transformation vectors (pMG101 and pMG103) for Phanerochaete chrysosporium were constructed, based on the ble phleomycin-resistance-encoding gene and a homologous histone H4 promoter. Transformation frequencies were 6–10 per μg of DNA. Transformed vector DNA could either exist as an unstable replicating plasmid or could be stably integrated. Integrated vector DNA from pMG101, which also contains a histone-encoding H3 gene in the promoter fragment, becomes methylated, resulting in inactivation of ble-dependent resistance. Plasmid pMG103, which lacks the H3, does not show methylation.

TFIID sequence recognition of the initiator and sequences farther downstream in Drosophila class II genes.

Immunopurified TFIID produces a large DNase I footprint over the hsp70, hsp26, and histone H3 promoters of Drosophila. These footprints span from the TATA element to a position approximately 35 nucleotides downstream from the transcription start site. Using a "missing nucleoside" analysis, four regions within the three promoters have been found to be important for TFIID binding: the TATA element, the initiator, and two regions located approximately 18 and 28 nucleotides downstream of the transcription start site. On the basis of the missing nucleoside data, the initiator appears to contribute as much to the affinity as the TATA element. However, there is weak conservation of the sequence in this region. To determine whether a preferred binding sequence exists in the vicinity of the initiator, the nucleotide composition of this region within the hsp70 promoter was randomized and then subjected to selection by TFIID. After five rounds of selection, the preferred sequence motif--G/A/T C/TAT/GTG--emerged. This motif is a close match to consensus sequences that have been derived by comparing the initiator region of numerous insect promoters. Selection of this sequence demonstrates that sequence-specific interactions downstream of the TATA element contribute to the interaction of TFIID on a wide spectrum of promoters.

Cyclosporine A inhibits the activity of a TATA box-binding protein that is required for transcription from the adenovirus major late promoter

Nuclear extracts from P1798 lymphoma cells support transcription from the adenovirus major late promotor (AdMLP) and the human histone H4 promoter. Nuclear extracts prepared from P1798 cells treated with 1 microgram/ml cyclosporine A for 24 h fail to support transcription from AdMLP, whereas transcription from the histone H4 promoter is unimpaired. Both control and cyclosporine-treated extracts contain proteins that interact with synthetic deoxyoligonucleotides that correspond to the CAAT box, TATA box, and upstream stimulatory element of AdMLP. Cyclosporine had no discernible qualitative or quantitative effect upon such DNA-protein interactions, as observed by gel mobility shift assays. Analysis of 5' deletion mutants of AdMLP indicates that deletion of sequences upstream of the TATA box reduces AdMLP transcription by only 50%. This observation suggests that cyclosporine A, which inhibits AdMLP transcription by > 90%, is unlikely to act through changes in the amount or activity of upstream activators such as upstream stimulatory factor- or CAAT box-binding proteins. On the other hand, deletion of TATA box sequences between -50 and -11 base pairs virtually eliminates transcription from AdMLP in vitro. A partially purified TFIID fraction was obtained from control P1798 nuclear extracts. The TFIID fraction reconstitutes transcription from AdMLP when added to extracts from cyclosporine A-treated cells. Recombinant TATA box-binding protein also reconstitutes transcription from AdMLP in cyclosporine A-treated extracts. These results are consistent with the hypothesis that cyclosporine A regulates the activity of a subset of general transcription factors which are required for initiation from some promoters (such as AdMLP) but not from others (such as histone H4).

A wheat histone H3 promoter confers cell division‐dependent and ‐independent expression of the gus A gene in transgenic rice plants

To investigate developmental regulation of wheat histone H3 gene expression, the H3 promoter, which has its upstream sequence to -1711 (relative to the cap site as +1), was fused to the coding region of the gus A gene (-1711H3/GUS) and introduced into a monocot plant, rice. Detailed histochemical analysis revealed two distinct types of GUS expression in transgenic rice plants; one is cell division-dependent found in the apical meristem of shoots and roots and in young leaves, and another is cell division-independent detected in flower tissues including the anther wall and the pistil. In this study, replication-dependent expression occurring in non-dividing cells which undergo endoreduplication could not be discriminated from strict replication-independent expression. The observed expression pattern in different parts of roots suggested that the level of the H3/GUS gene expression is well correlated with activity of cell division in roots. To identify 5' sequences of the H3 promoter necessary for an accurate regulation of the GUS expression, two constructs containing truncated promoters, -908H3/GUS and -185H3/GUS, were analyzed in transiently expressed protoplasts, stably transformed calli and transgenic plants. The results indicated that the region from -909 to -1711 contains the positive cis-acting element(s) and that the proximal promoter region (up to -185) containing the conserved hexamer, octamer and nonamer motifs is sufficient to direct both cell division-dependent and -independent expression. The use of the meristem of roots regenerated from transformed calli for the analysis of cell division-dependent expression of plant genes is discussed.

A short histone H3 promoter from alfalfa specifies expression in s-phase cells and meristems

Cell division-dependent activity of a histone H3 promoter from alfalfa (Medicago sativa L.) has been shown through the analysis of both transgenicNicotiana tabacum L. plants and aM. varia L. cell line. A chimeric gene was used to assay the activity of the histone H3 promoter in both transgenic systems. The chimeric gene was composed of 284 bp of 5′ upstream sequence from an alfalfa histone H3 genomic clone fused to theβ-glucuronidase coding region and nopaline synthase terminator. The 284 bp of histone H3 promoter sequence specified histochemically detectableβ-glucuronidase expression in the peripheral zone of the shoot apical meristem and the root tip of transgenic tobacco plants. Highβ-glucuronidase activity was as observed in young leaf and callus tissues. In protoplast-derived cells, an increased histone H3 promoter function was detected in 4- to 5-day old cultures and correlated with elevated incorporation of [3H]thymidine. Northern blot analysis of RNA samples from synchronized cell suspension cultures has revealed maximum accumulation of bothβ-glucuronidase and endogenous histone H3 mRNAs in cells at S phase. Whereas the abundance of endogenous histone H3 transcripts declined abruptly after S-phase, the reporter gene showed a more gradual decrease in transcript level after the reduction in the number of S-phase cells. The possible role of the short histone H3 promoter sequence in the regulation of S-phase-dependent expression and the involvement of the 3′ end region of histone H3 genes in mRNA stability will be discussed.