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Topography of the three late mRNA's of polyoma virus which encode the virion proteins
Abstract:
The three cytoplasmic polyadenylated mRNA's which separately encode the three capsid proteins (VP1, VP2, and VP3) of polyoma virus were mapped on the viral genome by one- and two-dimensional gel electrophoreses of nuclease S1-resistant RNA-DNA hybrids. The mRNA's, which we designated mVP1, mVP2, and mVP3 to indicate the coding functions deduced from the cosedimentation of the RNAs and the messenger activities, comprise an overlapping set of 3'-coterminal molecules which also share a heterogeneous family of noncoding 5'-terminal regions (Flavell et al., Cell 16:357--371, 1979; Legon et al., Cell 16:373--388, 1979). The three species differ in the length of the 3' colinear coding region which is spliced to the 5' leader sequences. The common polyadenylated 3' end maps at map unit 25.3. The 5' ends of the colinear bodies of mVP1, mVP3, and mVP2 map at 48.5, 59.5, and 66.5 map units, respectively. An examination of the polyoma virus DNA sequence (Arrand et al., J. Virol. 33:606--618, 1980) in the vicinities of splicing sites approximated by the S1 gel mapping data for sequences common to the ends of known intervening sequences allowed prediction of the precise splice points in polyoma virus late mRNA's. In all three cases, the leader sequences are joined to the mRNA bodies at least 48 nucleotides before the translational initiation codon used in each particular messenger. The start signal which functions in each mRNA is the first AUG (or GUG) triplet after the splice junction.
Insights
This study maps polyoma virus mRNA locations on the viral genome. Precise splice points for late mRNA were predicted, identifying leader sequences joined to mRNA bodies before translation initiation codons.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Polyoma virus encodes three capsid proteins (VP1, VP2, VP3) via distinct polyadenylated mRNA molecules.
- These mRNA molecules (mVP1, mVP2, mVP3) form an overlapping set with shared 5' noncoding regions and 3' coterminal ends.
- Understanding the precise genomic locations and splicing of these viral mRNAs is crucial for deciphering viral gene expression.
Purpose of the Study:
- To map the three cytoplasmic polyadenylated mRNA species encoding polyoma virus capsid proteins (VP1, VP2, VP3) onto the viral genome.
- To predict the precise splice points for polyoma virus late mRNA by integrating S1 gel mapping data with DNA sequence information.
- To elucidate the relationship between leader sequences and coding regions in these viral mRNAs.
Main Methods:
- Mapping of mRNA on the viral genome using one- and two-dimensional gel electrophoreses of nuclease S1-resistant RNA-DNA hybrids.
- Analysis of polyoma virus DNA sequence to identify potential splice sites.
- Integration of S1 gel mapping data with DNA sequence information to predict precise splice points.
Main Results:
- The 3' coterminal ends of the mRNA species map at map unit 25.3.
- The 5' ends of the coding regions for mVP1, mVP3, and mVP2 map at map units 48.5, 59.5, and 66.5, respectively.
- Precise splice points were predicted, revealing that leader sequences are joined to mRNA bodies at least 48 nucleotides upstream of the translational initiation codon.
Conclusions:
- The study successfully mapped the polyoma virus capsid protein mRNAs and predicted their precise splice points.
- The findings demonstrate a conserved mechanism for initiating translation in polyoma virus late mRNA, utilizing the first AUG/GUG triplet after the splice junction.
- This detailed mapping provides a foundational understanding of polyoma virus gene expression regulation at the mRNA level.