Regulation of Adenovirus Late Region 1 Splicing
(English)Manuscript (Other academic)
The major late transcription unit (MLTU) produces one pre-mRNA that is processed into more than 20 cytoplasmic mRNAs by alternative polyadenylation and extensive alternative 3' splice site usage. The alternative splicing of the MLTU is temporally regulated, resulting in the expression of only one mRNA, the L1 52,55K, before the onset of viral genome replication. The L1 unit also encodes the IIIa mRNA, the expression of which is highly regulated at the level of splicing. We have previously shown that the adenoviral L4-33K protein enhances IIIa splicing via the IIIa virus infection-dependent splicing enhancer element. In this study we show that serine to glycine mutations in the tiny RS domain of the L4-33K protein retain more activity in vivo compared to results obtained previously in vitro. In addition, it is also clear that these mutations in the RS domain affect the sub-cellular localization of L4-33K. Thus, the RS domain appears to contain a nuclear localisation signal that is dependent on the serine residues. In a previous report we showed that, in extracts prepared from adenovirus-infected cells, splicing is independent of the general splicing factor U2AF. In this study we also demonstrate that none of the tested U2AF-replacement candidate proteins (PUF60, Caper α, and Caper β) collaborate with L4-33K in the activation of IIIa splicing. It has been suggested that regulation of L1 alternative splicing does not require cis-competition between the 52.55K and IIIa 3' splice sites. We find that activity of the IIIa splice site increases considerably in the absence of cis-competition with the 52,55K splice site. Interestingly, this cis-competition is not virus-specific since this observation is reproducible in a transcription unit where the β-globin 3' splice site replaces the natural 52,55K 3' splice site. We conclude that L1 alternative splicing conforms to the general rule in that it ordinarily makes use of the proximal 3' splice site (52,55K), whereas activation of distal 3' splice site usage requires active intervention. In adenovirus this intervention is achieved by production of the L4-33K protein.
Adenovirus, L4-33K, Splicing, 3VDF
IdentifiersURN: urn:nbn:se:uu:diva-101308OAI: oai:DiVA.org:uu-101308DiVA: diva2:212566