Histone acetyltransferases (HAT) play a critical role in transcriptional control by relieving repressive effects of chromatin, and yet how HATs themselves are regulated remains largely unknown. Here, it is shown that Twist directly binds two independent HAT domains of acetyltransferases, p300 and p300/CBP-associated factor (PCAF), and directly regulates their HAT activities. The N terminus of Twist is a primary domain interacting with both acetyltransferases, and the same domain is required for inhibition of p300-dependent transcription by Twist. Adenovirus E1A protein mimics the effects of Twist by inhibiting the HAT activities of p300 and PCAF. These findings establish a cogent argument for considering the HAT domains as a direct target for acetyltransferase regulation by both a cellular transcription factor and a viral oncoprotein.

Coronaviruses possess the largest known RNA genome, a 27-to 32-kb (+)-strand molecule that replicates in the cytoplasm. During virus replication, a 3′ coterminal nested set of five to eight subgenomic (sg) mRNAs are made that are also 5′ coterminal with the genome, because they carry the genomic leader as the result of discontinuous transcription at intergenic donor signals during (−)-strand synthesis when templates for sgmRNA synthesis are made. An unanswered question is whether the sgmRNAs, which appear rapidly and abundantly, undergo posttranscriptional amplification. Here, using RT-PCR and sequence analyses of head-totail-ligated (−) strands, we show that after transfection of an in vitro-generated marked sgmRNA into virus-infected cells, the sgmRNA, like the genome, can function as a template for (−)-strand synthesis. Furthermore, when the transfected sgmRNA contains an internally placed RNA-dependent RNA polymerase templateswitching donor signal, discontinuous transcription occurs at this site, and a shorter, 3′ terminally nested leader-containing sgmRNA is made, as evidenced by its leader-body junction and by the expression of a GFP gene. Thus, in principle, the longer-nested sgmRNAs in a natural infection, all of which contain potential internal template-switching donor signals, can function to increase the number of the shorter 3′-nested sgmRNAs. One predicted advantage of this behavior for coronavirus survivability is an increased chance of maintaining genome fitness in the 3′ one-third of the genome via a homologous recombination between the (now independently abundant) WT sgmRNA and a defective genome.bovine coronavirus | discontinuous transcription | negative-strand RNA ligation | negative-strand RNA synthesis | severe acute respiratory syndrome B y virtue of an RNA-dependent RNA polymerase (RdRp) template switch, coronaviruses, which include the severe acute respiratory syndrome (SARS) virus, generate a 3′-coterminal nested set of subgenomic mRNAs (sgmRNAs) that also contain the leader of the genome (1). The leader is 65-90 nt long, depending on the species of coronavirus, and the template switch likely occurs during synthesis of (−)-strand templates for sgmRNA synthesis (2, 3) (Fig. 1, Upper), although some switching during (+)-strand synthesis (4) may occur as well (5). With few exceptions, sgmRNAs generated from 3′-proximal template-switching donor sites on the genome are progressively more abundant [up to 70-fold more at the peak time of RNA synthesis, at 6-8 h postinfection (6)] than those generated from 5′-proximal sites. The sgmRNAs are translated to virion structural proteins or to nonstructural accessory proteins, both of which may function as virulence factors or as inhibitors of host immune responses (7,8).The function of the common leader on sgmRNAs is not known, but we postulated that it [in its (−)-strand form, called the antileader] serves as a promoter for sgmRNA replication, providing a means for sgmRNA amplification (6, 9). The replication model was deemed feasible because the ant...

Structure-based stabilization of protein−protein interactions (PPIs) is a promising strategy for drug discovery. However, this approach has mainly focused on the stabilization of native PPIs, and non-native PPIs have received little consideration. Here, we identified a non-native interaction interface on the three-dimensional dimeric structure of the N-terminal domain of the MERS-CoV nucleocapsid protein (MERS-CoV N-NTD). The interface formed a conserved hydrophobic cavity suitable for targeted drug screening. By considering the hydrophobic complementarity during the virtual screening step, we identified 5benzyloxygramine as a new N protein PPI orthosteric stabilizer that exhibits both antiviral and N-NTD protein-stabilizing activities. X-ray crystallography and small-angle X-ray scattering showed that 5-benzyloxygramine stabilizes the N-NTD dimers through simultaneous hydrophobic interactions with both partners, resulting in abnormal N protein oligomerization that was further confirmed in the cell. This unique approach based on the identification and stabilization of non-native PPIs of N protein could be applied toward drug discovery against CoV diseases.

BackgroundTaiwan has been considered free from canine parvovirus type 2c (CPV-2c) based on the last report of canine parvovirus type 2 (CPV-2) surveillance. However, since January 2015, the first report of CPV-2c in a puppy has occurred in Taiwan. There is currently limited information about the CPV-2c variant in Taiwan. In the present study, we characterized the previously unidentified CPV-2c variant and investigated the distribution of CPV-2 variants in Taiwan.MethodsDuring January 2014 to April 2016, fecal or rectal swab samples from 99 dogs with suspected CPV-2 infection in Taiwan were collected. Eighty-eight were identified as being either CPV-2a, −2b or -2c variants positive by real-time PCR and sequence analysis.ResultsSequence analysis of the 88 isolates confirmed CPV-2c as the dominant variant (54.6 %), followed by CPV-2b (26.1 %) and CPV-2a (19.3 %). Phylogenetic analysis demonstrated that the recent CPV-2c variants are similar to the Chinese CPV-2c strain but can be considered as novel Asian CPV-2c isolates.ConclusionThe present study provides evidence for the existence of a novel CPV-2c variant in Taiwan.Electronic supplementary materialThe online version of this article (doi:10.1186/s12985-016-0620-5) contains supplementary material, which is available to authorized users.

The positive-strand coronavirus genome of ~30 kilobase in length and subgenomic (sg) mRNAs of shorter lengths, are 5’ and 3’-co-terminal by virtue of a common 5’-capped leader and a common 3’-polyadenylated untranslated region. Here, by ligating head-to-tail viral RNAs from bovine coronavirus-infected cells and sequencing across the ligated junctions, it was learned that at the time of peak viral RNA synthesis [6 hours postinfection (hpi)] the 3’ poly(A) tail on genomic and sgmRNAs is ~65 nucleotides (nt) in length. Surprisingly, this length was found to vary throughout infection from ~45 nt immediately after virus entry (at 0 to 4 hpi) to ~65 nt later on (at 6 h to 9 hpi) and from ~65 nt (at 6 h to 9 hpi) to ~30 nt (at 120-144 hpi). With the same method, poly(U) sequences of the same lengths were simultaneously found on the ligated viral negative-strand RNAs. Functional analyses of poly(A) tail length on specific viral RNA species, furthermore, revealed that translation, in vivo, of RNAs with the longer poly(A) tail was enhanced over those with the shorter poly(A). Although the mechanisms by which the tail lengths vary is unknown, experimental results together suggest that the length of the poly(A) and poly(U) tails is regulated. One potential function of regulated poly(A) tail length might be that for the coronavirus genome a longer poly(A) favors translation. The regulation of coronavirus translation by poly(A) tail length resembles that during embryonal development suggesting there may be mechanistic parallels.