Regulated splicing of adenovirus type 5 E4 transcripts and regulated cytoplasmic accumulation of E4 mRNA

Abstract

The E4 gene of human type C adenoviruses has been shown previously to give rise to an array of mRNAs via differential splicing. In this study, the pattern of expression of these mRNAs during lytic infection was examined, and two distinct temporal classes were defined. mRNAs of the early class were distinguished from those of the late class by the presence, in the early class, of a sequence in the 3' half of the mRNA that was removed as an intron in the late class. A single mRNA of the late class was found to show a strong dependence on the presence of the 55-kDa protein from region Elb and the open reading frame 6 protein from region E4 for its normal cytoplasmic accumulation. One feature of this mRNA that distinguishes it from other E4 mRNAs expressed at late times is the retention within it of an intron from the 5' half of E4; it may therefore be recognized as incompletely spliced by the host cell and retained in the nucleus. It is proposed that the Elb 55-kDa/E4 open reading frame 6 protein complex facilitates accumulation of this mRNA by overcoming this retention mechanism.

Deep splicing plasticity of the human adenovirus type 5 transcriptome drives virus evolution

“…coding for the same ORF as well as numerous transcripts that apparently do not code for any known proteins. This makes comparison with previous RNAse protection assay data, for example, highly problematic 30 .…”

A gene transfer vector-cell line system for complete functional complementation of adenovirus early regions E1 and E4

“…E4 proteins are involved in several levels of regulation of cellular and viral gene expression, viral DNA replication, late viral RNA accumulation, viral protein synthesis, host shutoff, virus assembly, E2 expression, and adeno-associated virus helper function (9,13,36,43). Several sets of differentially spliced mRNAs are generated from the E4 region during viral infection (6,8,40,41). Of the possible open reading frame (ORF) products encoded by the E4 region, only one, either ORF3 or ORF6, is absolutely required for viral growth in tissue culture (2,10,13,18).…”

Conditional repression of the E2 transcription unit in E1-E3-deleted adenovirus vectors is correlated with a strong reduction in viral DNA replication and late gene expression in vitro

“…3B). Transcription from the E4 region was analyzed with oligonu-cleotide probes directed against sequences upstream of the E4 poly(A) signal (positions 32940 to 32859) which are present on all E4 transcripts (7). A 2.3-kb RNA could be detected with expression levels unaffected by tetracycline (Fig.…”