Adenovirus L4-22K stimulates major late transcription by a mechanism requiring the intragenic late-specific transcription factor-binding site

• The adenovirus major late promoter (MLP) generates a primary transcript that undergoes a complex pattern of regulated alternative RNA splicing and polyadenylation events. The late-specific activation of the MLP requires binding of two infected-cell specific transcription factor complexes, DEF-A and DEF-B, to the so-called DE sequence located downstream of the MLP start site. Previous studies have shown that DEF-B is a homodimer of the viral IVa2 protein and suggested that DEF-A is a heterodimer of IVa2 and an unknown protein. Here we have searched for a possible DEF-A candidate protein. The adenovirus L4-33K protein functions as a virus-encoded alternative RNA splicing factor, stimulating cytoplasmic accumulation of most late viral mRNAs. Interestingly, the L4 region also encodes for a second related protein, L4-22K, which share the 105 amino-terminal amino acids with L4-33K. Here we show that L4-22K both in vivo and in vitro stimulates transcription from the MLP in a DE sequence dependent manner. We also show that the viral pIX promoter is a natural target, activated by L4-22K. Interestingly, the position of the L4-22K DNA binding site in a promoter does not appear to be critical for function. Thus, tethering L4-22K, as a BPV E2 DNA binding domain fusion protein either to a position upstream or downstream of the MLP start site, or upstream of a minimal E1B promoter, resulted in an activation of transcription. Collectively, our results are compatible with the hypothesis that L4-22K may be the elusive component of DEF-A that partakes in activation of the MLP.

Nyckelord

Adenovirus

L4-22K

MLP

transcription

DE elements

MEDICINE

MEDICIN

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