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CUG initiation codon used for the synthesis of a cell surface antigen coded by the murine leukemia virus
A C Prats1, G De Billy, P Wang
1Labo-Retro, Centre de Recherche de Biochimie, Génétique Cellulaires du CNRS, France.
Abstract:
Murine leukemia virus (MuLV) codes for two precursors of the group-specific antigens, Pr65gag and Pr75gag, in vivo. While Pr65gag is the precursor to the virion structural proteins, Pr75gag undergoes glycosylation and is found on the surface of the infected cell as gp85gag, and it is thought to play a role in virus maturation and spread. Pr65gag synthesis starts at an AUG codon within a favourable initiation context (AAUAUGG at positions 618 to 624). The gp85gag start codon is upstream but its precise location is not known. To map the initiation codon of gp85gag, we used deletion and site-directed mutagenesis of the leader sequence of MuLV RNA and in vitro translation of the RNAs. Synthesis of the MuLV gp85gag protein appears to be initiated at a CUG codon located within a favourable context (ACCCUGG at positions 354 to 359 for Moloney-MuLV). The possible function of gp85gag was investigated by expressing Moloney-MuLV and Friend-MuLV proviral DNA and mutants deficient for gp85gag synthesis in mouse and rat cells. The results indicate that the gp85gag protein probably facilitates the spread of virus infection in tissue culture.
Insights
Murine leukemia virus (MuLV) produces two gag precursors. The gp85gag protein, initiated at a CUG codon, appears to facilitate virus spread in cell culture.
Area of Science:
- Virology
- Molecular Biology
- Retroviral Research
Background:
- Murine leukemia virus (MuLV) encodes two gag precursors: Pr65gag and Pr75gag.
- Pr65gag is essential for virion structural proteins, while glycosylated Pr75gag (gp85gag) is found on infected cell surfaces and implicated in virus spread.
- The precise initiation codon for gp85gag was previously unknown.
Purpose of the Study:
- To map the initiation codon of the gp85gag protein in MuLV.
- To investigate the functional role of gp85gag in virus infection and spread.
Main Methods:
- Deletion and site-directed mutagenesis of MuLV RNA leader sequences.
- In vitro translation of modified MuLV RNAs.
- Expression of Moloney-MuLV and Friend-MuLV proviral DNA, including gp85gag-deficient mutants, in mouse and rat cells.
Main Results:
- The gp85gag protein is initiated at a CUG codon within a favorable context (ACCCUGG at positions 354-359 for Moloney-MuLV).
- Expression of gp85gag in cultured cells suggests a role in facilitating virus spread.
- Mutants deficient in gp85gag synthesis were used to assess its function.
Conclusions:
- The initiation codon for MuLV gp85gag has been identified as a CUG codon.
- The gp85gag protein likely plays a significant role in promoting the spread of MuLV infection in tissue culture.