Order of polyadenylic acid addition and splicing events in early adenovirus mRNA formation
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Abstract:
A study of the processing of mRNA from two early adenovirus type 2 transcription units (regions 2 and 4 of adenovirus type 2 genome; [J. Flint, Cell 10:153--166, 1977]) revealed that polyadenylic acid [poly(A)] was added in most if not all cases to an unspliced nuclear RNA molecule whose coordinates extended from the apparent initiation site for RNA synthesis to the single poly(A) site in each transcription unit. An intermediate RNA molecule in the processing of the mRNA for the 72,000-M, single-stranded DNA binding protein showed that the first of the two intervening sequences, the one closest to the 5' end of the molecule, was removed first at least in the majority of the processed molecules. Finally, in cells labeled for 10 min and then treated with actinomycin D to stop further RNA synthesis, the majority, if not all, of the poly(A)-terminated nuclear RNA specific for region 2 was successfully processed and transported to the cytoplasm.
Insights
Adenovirus mRNA processing involves adding polyadenylic acid [poly(A)] to unspliced nuclear RNA. The first intervening sequence is removed early, and poly(A)-terminated RNA is efficiently processed and transported to the cytoplasm.
Area of Science:
- Molecular Biology
- Virology
- Gene Expression
Background:
- Adenovirus type 2 transcription units are crucial for viral gene expression.
- Understanding mRNA processing is key to deciphering viral replication and host interactions.
Purpose of the Study:
- To investigate the processing of mRNA from adenovirus type 2 transcription units.
- To elucidate the sequence of splicing events and polyadenylation during mRNA maturation.
Main Methods:
- Analysis of nuclear RNA from adenovirus type 2 infected cells.
- Identification of intermediate RNA species during mRNA processing.
- Use of actinomycin D to inhibit further RNA synthesis and study processing kinetics.
Main Results:
- Polyadenylic acid [poly(A)] is added to unspliced nuclear RNA transcripts.
- The 5' proximal intervening sequence is removed preferentially during early processing.
- Poly(A)-terminated nuclear RNA is efficiently processed and exported to the cytoplasm.
Conclusions:
- Adenovirus mRNA processing is a coordinated process involving polyadenylation and splicing.
- Early removal of the 5' intervening sequence facilitates subsequent processing steps.
- Efficient cytoplasmic transport of mature mRNA is essential for viral protein synthesis.