(2) EBOV ja MARV RNA editointi (jatkoa) . Uusinta käsitystä asiasta.

Johdanto,  INTRODUCTION

The recent outbreak in West Africa of Zaire ebolavirus (EBOV) is of unprecedented scope in terms of the number of cases and geographic breadth (1). This event, coupled with the increased frequency of
outbreaks caused by the Filoviridae family, which includes the ebolaviruses and marburgviruses (MARV), highlights the need for a complete understanding of filovirus replication (2,–4).

Previous studies have provided a detailed description of EBOV and MARV genome transcription and replication strategies (5,–7). The filoviruses possess nonsegmented negative-sense (NNS) viral RNA (vRNA) genomes of approximately 19 kb in length. 

Filoviral genome replication results in the production of full-length, positive-sense antigenomic RNA and negative-sense genomic RNA (7, 8).

 In contrast, filovirus transcription likely proceeds along the viral genomic RNA template via a stop-start mechanism that results in the production of individual 5′-7-methylguanosine (m⁷G)-capped, 3′-polyadenylated mRNAs (9,–11). This is analogous to the transcription of several other NNS RNA viruses, such as vesicular stomatitis virus (VSV) (12).

 Transcripts are produced from each of the nucleoprotein (NP), VP35, VP40, viral glycoprotein (GP), VP30, VP24, and large (L) protein genes. 

For EBOV, there are seven transcription start signals of 12 nucleotides (nt) in length that differ at only 1 nt; transcriptional stop signals are present for each gene and are also conserved, and each gene possesses, on the genomic vRNA, a poly(U) stretch that serves as a signal for polyadenylation (6).

 Notably, the VP24/L junction contains two stop signals (13), but most transcription stops at the first stop signal (14).

 For MARV, the transcriptional start signals are also 12 nt in length with minor variations depending on the specific gene, and the consensus stop signal is also conserved. Between NNS RNA virus start and stop sequences are intergenic regions that differ in length.

Whereas most filoviral genes have been reported to yield a single mRNA species encoding a single major translation product, the EBOV GP gene is an exception. The major mRNA species produced by the GP gene encodes soluble glycoprotein (sGP). However, two additional proteins, the full-length GP (a structural protein that serves as the viral attachment and fusion protein) and ssGP (a protein of unknown function) are produced via an RNA editing process.

This RNA editing is carried out by the viral polymerase, such that one or more non-template-encoded A nucleotides are inserted within the EBOV GP open reading frame (ORF) at a stretch of seven U nucleotides spanning genome positions 6918 to 6925 (15, 16).

Therefore, RNA editing by the viral polymerase increases the number of proteins produced by a limited number of viral genes (17, 18).

EBOV genomin replikaatiosta lisäoivalluksia tältä vuodelta

LÄHDE: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4222107/

Deep Sequencing Identifies Noncanonical Editing of Ebola and Marburg Virus RNAs in Infected Cells

Reed S. Shabman, Omar J. Jabado, [...], and Christopher F. Basler

Additional article information

Tiivistelmää, ABSTRACT

•  Zairen ebolaviruksen  tai  Angolan  marburgviruksen kantojen   tuottamien RNA-produktien perusteellisempi sekvensointi antaa tunnistaa uudentyyppisen virus- ja solumekanismin, joka erilaistaa viruksen koodaavia ja nonkoodaavia  mRNA ja RNA-sekvenssejä.

Deep sequencing of RNAs produced by Zaire ebolavirus (EBOV) or the Angola strain of Marburgvirus (MARV-Ang) identified novel viral and cellular mechanisms that diversify the coding and noncoding sequences of viral mRNAs and genomic RNAs. 

•  Tiedemiehet tunnistivat aiemmin osoittamattomia kohtia EBOV ja  MARV-Ang mRNA:sta, joissa ilmeinen kotranskriptionaalinen editointi on johtanut non-templaatti-peräisesti koodautuneitten nukleotiditähteiden  lisäämiseen EBOV GP mRNA:han, , MARV-Ang nukleoproteiini (NP)mRNA:hanja MARV-Ang polymeraasin(L) mRNA:han  siten, että uudenlaisia virustranslaatiotuotteita saattaisi ilmetä.

We identified previously undescribed sites within the EBOV and MARV-Ang mRNAs where apparent cotranscriptional editing has resulted in the addition of non-template-encoded residues within the EBOV glycoprotein (GP) mRNA, the MARV-Ang nucleoprotein (NP) mRNA, and the MARV-Ang polymerase (L) mRNA, such that novel viral translation products could be produced.

•  Lisäksi tiedemiehet osoittivat, että hyvin luonnehditun EBOV  glykoproteiini (GP) -mRNA:n  editointikohta   modifioituu tiheästi virusgenomin RNA:n replikaaiton aikana. Lisäksi nämä  editoimisen kuumat pisteet edustavat sellaisia kohtia, joissa on ilmeistä adenosiinideaminaasiaktiivisuutta havaittavissa MARV-Ang NP:n  3 -prim-translatoimattomassa alueessa. Nämä tutkimukset  tunnistavat uudenlaisen filovirus-isäntä- interaktion ja paljastavat  filovirusgeenituotteissa esiintyvän  tuotannon  suurempaa  diversiteettiä  kuin aiemmin on arvioitukaan.

 Further, we found that the well-characterized EBOV GP mRNA editing site is modified at a high frequency during viral genome RNA replication. Additionally, editing hot spots representing sites of apparent adenosine deaminase activity were found in the MARV-Ang NP 3′-untranslated region. These studies identify novel filovirus-host interactions and reveal production of a greater diversity of filoviral gene products than was previously appreciated.

Mikä tämän löydön merkitys on? IMPORTANCE

•  Tässä tutkimuksessa on tunnistettu uudenlainen mekanismi, jolla  Ebola- ja Marburg-virusten mRNA   muuntaa  proteiinia koodaavia kykyjään. Sentakia filovirusgeenin ilemenmä on monimutkaisempaa ja  diversiteetiltään runsaamaa, kuin aiemmin on oivallettu. Näistä havainnoista saa uusia  suuntia filovirusgeenin expression säätelyn käsittämsieen.

This study identifies novel mechanisms that alter the protein coding capacities of Ebola and Marburg virus mRNAs. Therefore, filovirus gene expression is more complex and diverse than previously recognized. These observations suggest new directions in understanding the regulation of filovirus gene expression.

• Johdanto, Introduction (jatkuu 2)