The development of an induced transcript environment was investigated at the supramolecular level through comparative localization of the human cytomegalovirus immediate early (IE) transcripts and specific nuclear domains shortly after infection. Compact aggregates of IE transcripts form only adjacent to nuclear domain 10 (ND10), and the viral protein IE86 accumulates exclusively juxtaposed to the subpopulation of ND10 with transcripts. The stream of transcripts is funneled from ND10 into the spliceosome assembly factor SC35 domain through the accumulation of IE86 protein, which recruits some components of the basal transcription machinery. Concomitantly the IE72 protein binds to ND10 and later disperses them. The domain containing the zinc finger region of IE72 is essential for this dispersal. Positional analysis of proteins IE86 and IE72, IE transcripts, ND10, the spliceosome assembly factor SC35, and basal transcription factors defines spatially and temporally an immediate transcript environment, the basic components of which exist in the cell before viral infection, providing the structural environment for the virus to usurp.

Human cytomegalovirus immediate-early (IE) region 2 (0.732 to 0.740 map unit) begins 35 nucleotides downstream of IE region 1 (Stenberg et al., J. Virol. 49:190-199, 1984). A series of mRNAs that have different splicing patterns are transcribed from region 2. There is an unspliced 1,589-nucleotide exon present in minor amounts and two spliced exons (836 and 289 nucleotides) present in larger amounts. The IE region 2 exons were found to be spliced onto the first three exons of region 1. Therefore, under IE conditions the region 1 promoter-regulatory region can promote transcription of region 2. Promoter sequences (i.e., CAAT and TATA boxes) are found upstream of the 5' end of IE region 2 but presumably function poorly at IE times after infection. The transcriptional regulation of these IE genes and the possible functional roles of the proteins are discussed. We postulate that a series of unique but related proteins are made from the region 2 transcripts. Some of these proteins should contain the same 169 amino-terminal residues as the major IE 72-kilodalton protein encoded by IE region 1 (Stenberg et al., J. Virol. 49:190-199, 1984). Variations in the amino acid sequences of the region 2 proteins could occur at either the amino terminus, the carboxy terminus, or both termini.

The most abundant species of human cytomegalovirus (Towne) immediate early polysome-associated RNA originates from a region of ca. 2.8 kilobases (0.739 to 0.755 map units) within the XbaI-E DNA fragment. These sequences code for a 1.95-kilobase mRNA and are referred to as immediate early coding region one (M. F.

trans activation of promoters by viral regulatory proteins provides a useful tool to study coordinate control of gene expression. Immediate-early (IE) regions 1 and 2 of human cytomegalovirus (CMV) code for a series of proteins that originate from differentially spliced mRNAs. These IE proteins are proposed to regulate the temporal expression of the viral genome. To examine the structure and function of the IE proteins, we used linker insertion mutagenesis of the IE gene region as well as cDNA expression vector cloning of the abundant IE mRNAs. We showed that IEl and IE2 proteins of CMV exhibit promoter-specific differences in their modes of action by either trans activating early and IE promoters or repressing the major IE promoter (MIEP). Transient cotransfection experiments with permissive human cells revealed a synergistic interaction between the 72-and the 86-kilodalton (kDa) IE proteins in trans activating an early promoter. In addition, transfection studies revealed that the 72-kDa protein was capable of trans activating the MIEP. In contrast, the 86-kDa protein specifically repressed the MIEP and this repression was suppressed by the 72-kDa protein. Furthermore, observations based on the primary sequence structure revealed a modular arrangement of putative regulatory motifs that could either potentiate or repress gene expression. These modular domains are either shared or unique among the IE proteins. From these data, we propose a model for IE protein function in the coordinate control of CMV gene expression.

Expression of RNA and protein from the human cytomegalovirus immediate-early (IE) gene region (map units 0.732 to 0.751) was analyzed at early and late times after infection. The level of RNA present at late times (48 to 72 h after infection) was significantly higher than that present at IE times (5 h after infection). The profile of IE RNA in the cytoplasm of infected cells was different from that previously reported on polysomes (R. M.

The immediate early genes of human cytomegalovirus were characterized according to map location, RNA transcripts, and translation products. Three regions in the large unique component (0.709 to 0.751 map units) were transcribed in the presence of an inhibitor of protein synthesis (anisomycin). A single size class of polyadenylated mRNA, 1.95 kilobases (kb), was transcribed abundantly relative to the other size classes. The predominant 1.95-kb viral RNA was transcribed from right to left on the prototype arrangement of the viral genome and spanned a region of approximately 2.8 kb (0.739 to 0.751 map units). This mRNA codes for a 75,000-dalton protein that represents the predominant immediate early protein detected in infected cells. Immunoprecipitation of viral proteins synthesized in vitro as well as in vivo demonstrated that the predominant immediate early protein is synthesized as a protein of 75,000 daltons, but is presumably modified in vivo, resulting in a broad banding pattern ranging from 75,000 to 68,000 daltons. A different immediate early viral gene (0.732 to 0.739 map units) is transcribed from left to right at relatively low levels. The 3' ends of the above viral RNAs terminate at approximately 230 base pairs apart in the region of approximately 0.739 map units. Five RNA size classes ranging from 2.25 to 1.10 kb were detected, but the 1.75-kb and 1.40-kb RNA size classes were more abundant from this region. At least four minor proteins are coded by these mRNAs, with apparent molecular weights ranging from 56,000 to 16,500. Last, a 1.95-kb mRNA was transcribed from a third region (0.709 to 0.728 map units). This viral mRNA was present at relatively low concentration and coded for a minor protein of 68,000 daltons. Since immediate early gene expression of human cytomegalovirus is dominated by the synthesis of an mRNA from the region of 0.739 to 0.751 map units that codes for the predominant immediate early protein found in the infected cell, we hypothesize that this protein is the major regulatory protein influencing the switch from restricted to extensive transcription.

The DNA templates containing immediate early (IE) genes of human cytomegalovirus (CMV) were transcribed in vitro by using a HeLa cell extract. When IE region 1, 2, and 3 were used, transcription was detected qualitatively only from IE region 1. Transcription was detected with DNA representing IE region 2 when the IE region 1 promoter was not present. DNA sequence analysis of the upstream regulatory region of IE region 1 detected two distinct repeats of 19 and 18 nucleotides, both being repeated four times. A putative cruciform structure could form through the surrounding sequences with each 18-nucleotide repeat being located in the unpaired region. The potential secondary structure and the repeat sequences in the regulatory region of IE region 1 are presumably related to the high level of transcription of this IE gene.Human cytomegalovirus (CMV), a member of the' herpesvirus classification group, has a large double-stranded DNA genome of 240 kilobases (kb). The viral genome consists of a long-and short unique region flanked by differept repeat sequences 'that are inverted relative to each other. Four genome arrangements, resulting from the possible combination of inversions of the two sections of the genome, are present in DNA preparations in approximately equal amounts (1-7).At immediate early (IE) times after infection-i.e., in the absence of de novo viral protein synthesis, 88% or more of the viral RNA originates from a region in the long unique component of the viral genome (6,8,9) In Vitro Transcription and RNA Fractionation. In vitro transcription was as described by Manley et al. (14). Recombinant plasmids cut with various restriction enzymes to generate linear templates were at a concentration of 100 ig per ml. Some reactions contained a-amanitin (1 pg/ml; Sigma) to inhibit RNA polymerase II activity. The 32P-labeled RNA was subjected to electrophoresis in 1.5% agarose gels containing 10 mM methylmercury (II) hydroxide as described by Bailey and Davidson (15). Molecular weight standards were 23S (3.3 kb) and 16S (1.7 kb) Escherichia coli rRNA (16), 28S (5.3 kb) and 18S (2.0 kb) human' cell rRNA (17), and approximately 0.160 kb tRNA. To visualize the RNA, the slab gels were stained in a solution containing 0.5 M ammonium acetate, 0.005 M 2-mercaptoethanol, and 1 ,ug of ethidium bromide per ml. The gels were dried and exposed to Kodak XOmat AR film. RNA sizes were interpolated from a standard 659The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C.- §1734 solely to indicate this fact.

To better understand the regulation of late gene expression in human cytomegalovirus (CMV)-infected cells, we examined expression of the gene that codes for the 65-kilodalton lower-matrix phosphoprotein (pp65). Analysis of RNA isolated at 72 h from cells infected with CMV Towne or ts66, a DNA-negative temperaturesensitive mutant, supported the fact that pp65 is expressed at low levels prior to viral DNA replication but maximally expressed after the initiation of viral DNA replication. To investigate promoter activation in a transient expression assay, the pp65 promoter was cloned into the indicator plasmid containing the gene for chloramphenicol acetyltransferase (CAT). Transfection of the promoter-CAT construct and subsequent superinfection with CMV resulted in activation of the promoter at early times after infection. Cotransfection with plasmids capable of expressing immediate-early (IE) proteins demonstrated that the promoter was activated by IE proteins and that both IE regions 1 and 2 were necessary. Analysis of promoter deletion mutants indicated that the 5' minimal sequence required for activation is-61 from the CAP site (+ 1) and that an 8-base-pair sequence located at-51 to-58 is necessary for activation of the pp65 promoter. This sequence is repeated once at +93 and is found as an inverted repeat at +67. These studies suggest that interactions between IE proteins and this octamer sequence may be important for the regulation and expression of this CMV gene.