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Characterization of an intergroup serological mutant from group II RNA phage GA
Abstract:
Starting from the group II RNA phage GA which has an amber mutation in the maturation protein cistron, a spontaneous mutant of group II phage GA, whose serological and electrophoretic properties became similar to those of group I phage MS2, was isolated and analyzed. The mutant has now become sensitive to anti-MS2 serum and resistant to anti-GA serum. Analysis of the nucleotide sequence of the coat protein gene revealed that G----A transition was the main change. The deduced amino acid sequence showed that five amino acids were substituted in the mutant, and three of the five became identical to MS2, resulting in increased molecular weight of the coat protein. However, it did not complement MS2. These results suggested that the serological change from group II phage GA type to group I phage MS2 type is induced spontaneously at high frequency by minor nucleotide changes in coat protein gene, and confirmed the previous results at the RNA level that MS2 and GA were related although the closeness between them seems somewhat remoter than that of groups III and IV (18, Inokuchi et al, unpublished data for the nucleotide sequence of group IV phage SP).
Insights
A spontaneous mutation in RNA phage GA
Area of Science:
- Molecular biology
- Virology
- Genetics
Background:
- RNA phage GA, a group II phage, possesses an amber mutation in its maturation protein gene.
- Serological and electrophoretic analysis differentiates RNA phage groups.
Purpose of the Study:
- To investigate the genetic basis of serological changes in RNA phage GA.
- To analyze a spontaneous mutant of phage GA exhibiting properties similar to group I phage MS2.
Main Methods:
- Isolation and characterization of a spontaneous RNA phage GA mutant.
- Nucleotide sequence analysis of the coat protein gene.
- Deduced amino acid sequence analysis.
- Complementation tests.
Main Results:
- A spontaneous mutant of phage GA showed sensitivity to anti-MS2 serum and resistance to anti-GA serum.
- A G-to-A transition in the coat protein gene was identified as the primary genetic change.
- Three out of five substituted amino acids in the mutant coat protein became identical to those of MS2, increasing its molecular weight.
- The mutant did not complement MS2, indicating functional differences despite serological similarities.
Conclusions:
- Minor nucleotide changes in the coat protein gene can induce significant serological alterations in RNA phages at high frequency.
- The study confirms a relationship between MS2 and GA phages at the RNA level.
- The findings suggest that MS2 and GA are related but distinct, with a more distant relationship than observed between other phage groups.
