Avian sarcoma virus gag precursor polypeptide is not processed in mammalian cells

Area of Science:

• Virology
• Molecular Biology
• Cell Biology

Background:

• Rous sarcoma virus (RSV) is an avian retrovirus that transforms mammalian cells.
• Intracellular gag proteins are essential structural components of retroviral virions.
• Understanding gag protein processing in non-permissive cells provides insights into viral replication.

Purpose of the Study:

• To investigate the processing of avian gag proteins in mammalian cell lines transformed by RSV.
• To determine if gag precursor polypeptides are matured into functional viral proteins in these cells.
• To explore the association between gag protein processing and virion assembly.

Main Methods:

• Radioimmune assay to detect gag antigens in transformed mammalian cells.
• Protein blotting from polyacrylamide gels to analyze viral polypeptide sizes.
• Analysis of gag precursor Pr76 and Pr180 (reverse transcriptase precursor) synthesis.
• Use of protease inhibitors to enhance recovery of Pr76.

Main Results:

• All examined mammalian cell lines contained gag antigens.
• Synthesized Pr76, the gag precursor, was detected but not processed into mature proteins.
• Pr180, the reverse transcriptase precursor, was also synthesized in some cell lines.
• Protease inhibitors, like N-ethylmaleimide, enhanced Pr76 recovery.

Conclusions:

• Mammalian cells transformed by RSV synthesize but do not process avian gag precursor proteins.
• The lack of processing suggests that cleavage and virion assembly are intrinsically linked.
• This study highlights the block in RSV replication and maturation in mammalian cells.