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Comparative Study
. 2019 Feb 12;10(1):e02047-18.
doi: 10.1128/mBio.02047-18.

Nucleotide Resolution Comparison of Transcription of Human Cytomegalovirus and Host Genomes Reveals Universal Use of RNA Polymerase II Elongation Control Driven by Dissimilar Core Promoter Elements

Affiliations
Comparative Study

Nucleotide Resolution Comparison of Transcription of Human Cytomegalovirus and Host Genomes Reveals Universal Use of RNA Polymerase II Elongation Control Driven by Dissimilar Core Promoter Elements

Mrutyunjaya Parida et al. mBio. .

Abstract

The large genome of human cytomegalovirus (HCMV) is transcribed by RNA polymerase II (Pol II). However, it is not known how closely this betaherpesvirus follows host transcriptional paradigms. We applied PRO-Seq and PRO-Cap methods to profile and quantify transcription initiation and productive elongation across the host and virus genomes in late infection. A major similarity between host transcription and viral transcription is that treatment of cells with the P-TEFb inhibitor flavopiridol preempts virtually all productive elongation, which otherwise covers most of the HCMV genome. The deep, nucleotide resolution identification of transcription start sites (TSSs) enabled an extensive analysis of core promoter elements. An important difference between host and viral transcription is that initiation is much more pervasive on the HCMV genome. The sequence preferences in the initiator region around the TSS and the utilization of upstream T/A-rich elements are different. Upstream TATA positions the TSS and boosts initiation in both the host and the virus, but upstream TATT has a significant stimulatory impact only on the viral template. The major immediate early (MIE) promoter remained active during late infection and was accompanied by transcription of both strands of the MIE enhancer from promoters within the enhancer. Surprisingly, we found that the long noncoding RNA4.9 is intimately associated with the viral origin of replication (oriLyt) and was transcribed to a higher level than any other viral or host promoter. Finally, our results significantly contribute to the idea that late in infection, transcription takes place on viral genomes that are not highly chromatinized.IMPORTANCE Human cytomegalovirus infects more than half of humans, persists silently in virtually all tissues, and produces life-threatening disease in immunocompromised individuals. HCMV is also the most common infectious cause of birth defects and the leading nongenetic cause of sensorineural hearing loss in the United States. Because there is no vaccine and current drugs have problems with potency, toxicity, and antiviral drug resistance, alternative treatment strategies that target different points of viral control are needed. Our current study contributes to this goal by applying newly developed methods to examine transcription of the HCMV and host genomes at nucleotide resolution in an attempt to find targetable differences between the two. After a thorough analysis of productive elongation and of core promoter element usage, we found that some mechanisms of regulating transcription are shared between the host and HCMV but that others are distinctly different. This suggests that HCMV transcription may be a legitimate target for future antiviral therapies and this might translate to other herpesviruses.

Keywords: P-TEFb; PRO-Seq; RNA polymerase II; RNA4.9; core promoter elements; cytomegalovirus.

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Figures

FIG 1
FIG 1
PRO-Seq from HFF infected with HCMV. (A) Nuclei were harvested at 4 h postinfection (hpi) with the TB40E strain (red) or at 96 hpi with the Towne strain (blue). During the last hour, cells were also treated with 0.1% DMSO ± 1 µM flavopiridol. PRO-Seq reads were aligned to the HCMV Towne strain genome (GenBank accession number FJ616285.1) and visualized in a UCSC Genome Browser track hub (top, forward strand; bottom, reverse strand). All tracks range from 0 to the indicated number of reads. Coding regions and the origin of lytic replication (red triangle) are shown below. (B) Pairwise correlation analysis of Towne or Towne BAC PRO-Seq data sets obtained 96 hpi of HFF. Numbers of forward and reverse reads from control and flavopiridol-treated cells were compared for each nucleotide across 212,000 bp of shared genome. Spearman coefficients are indicated.
FIG 2
FIG 2
Prevalence of flavopiridol-sensitive productive elongation. (A) UCSC Genome Browser views of sample regions of PRO-Seq from two biologically distinct infections (Towne and Towne BAC) with ROPE analyses for forward (Fw) and reverse (Rv) reads derived from the difference between the control and flavopiridol (Flavo) data sets. Average reads across the ROPEs are broken into quartiles and shaded (black is the top 25%). (B) Metagene analyses from the host before (29,838 TSRs) and after (20,784 TSRs) infection with HCMV (1,211 TSRs) comparing control and flavopiridol data normalized across the region shown.
FIG 3
FIG 3
Regulated transcription of major immediate early (MIE) promoters. (A) PRO-Seq and PRO-Cap from HFF infected with HCMV strain Towne 96 hpi. All tracks range from 0 to the indicated number of reads and are not otherwise normalized. Coding regions (black, thick) from GenBank (accession number FJ616285.1), IE1- and IE2-p86 5′ untranslated regions (UTRs) (black, thin) and potential coding regions for IE2-p60 and IE2-p40 (gray) (33, 64), and the MIE enhancer region (white) (21) are identified. MIE promoter and enhancer TSSs are indicated. E1 is on the forward strand, while P1 to P5 and E2 are on the reverse strand. (B) Western blot of IE2 isoforms, late HCMV tegument protein pp28, and actin and 8% SDS-PAGE. (C) Base composition of MIE promoters P1 to P5. Highlighted are major TSSs (green) and TATA (blue) or TATT (red) elements starting 34 to 30 bp upstream. P4 has two major start sites: one presumably driven by TATA and the other driven by TATT.
FIG 4
FIG 4
Regulated transcription around oriLyt and RNA4.9. (A) PRO-Seq from control and flavopiridol-treated HFF infected with HCMV strain Towne at 96 hpi. All tracks range from 0 to the indicated number of reads and are not otherwise normalized. Essential regions (white) within oriLyt (pink) (39) are indicated. Potential G quadruplexes are indicated (orange, forward strand; green, reverse strand). (B) HeLa nuclear extracts and the indicated amounts of soluble MIE (508-nt runoff) or the pUC19-RNA4.9 promoter template cut with BamHI (350-nt runoff) or HindIII (380-nt runoff) were preincubated for 30 min, pulsed for 30 s with limiting [α-32P]CTP, and chased for 5 min and subject to 6% urea-PAGE. (C) Forward-strand base composition of potential G quadruplexes.
FIG 5
FIG 5
Sequence architecture of host and HCMV promoters. (A) Sequences and PRO-Cap signal around the MaxTSS within human control and flavopiridol TSRs, as well as of HCMV control and flavopiridol TSRs. Heatmaps were sorted by PRO-Cap signal of the MaxTSS. Bases: G, yellow; A, gray; T, red; C, blue. (B) Base composition probabilities for all TSRs in panel A from bp −50 to +50.
FIG 6
FIG 6
Influence of upstream promoter elements on Pol II initiation. (A) Human and 96-hpi HCMV TSRs with the initial base of TATA (left) or TATT (right) starting −40 to −21 bp upstream of the MaxTSS were selected, and sequences and PRO-Cap signal around the MaxTSS were plotted. Heatmaps were sorted by upstream promoter element distance. Bases: G, yellow; A, white; T, red; C, blue. (B) Influence of upstream TATA or TATT distance on Pol II initiation. The human and HCMV TSRs analyzed in panel A with the initial base of TATA (left) or TATT (right) starting −40 to −21 bp upstream of the MaxTSS were selected, and the average number of PRO-Cap reads originating from these MaxTSS were plotted using R boxplot. Box boundaries are drawn at the 25th and 75th percentiles, whiskers are 1.5 times the interquartile range, and the median is indicated. Outliers are not shown. (C) WebLogos for the indicated sets of genes.

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