Anomalous Behavior of Adenovirus L4-33K Mutant Protein
Mohammad Feraz Ahsan
Journal Title:Acta Scientific Microbiology
The late genes of adenovirus are transcribed from the major late transcription unit (MLTU), generating mRNA through L1 to L5. L4-33K protein is RNA splicing factor responsible for early to late switch in L1 alternative splicing. The L1-52,55K mRNA is produced during both early and late after infection, whereas L1-IIIa mRNA at late phase. L4-33K when phosphorylated by DNA-dependent protein kinase (DNA-PK) has an inhibitory effect on the temporal switch in L1 alternative RNA splicing, whereas phosphorylation with protein kinase A (PKA) has an enhancer effect on L1-IIIa splicing. The C-terminal region of L4-33K is conserved and responsible for splicing, nuclear localization and other functional activities. Mutational studies replacing serine with glycine in L4-33K, referred to as S176G, S189G, S196G did not hamper above functionality, but mutation at position 192 abolished the L4-33K splicing enhancer activity and nuclear localization. Here we show the posttranslational effect of these proteins against DNA-PK and PKA; all the mu-tants showed hypophosphorylation with DNA-PK and PKA, except S192G, which unusually showed hyperphosphorylation up to 2.63 times of the wild type L4-33K against DNA-PK, justifying earlier findings. This unusual result may be due to drastic misfolding of S192G exposing other phosphorylating residues. It would be interesting to carry out structural analysis of this protein during native and phosphorylated state.