Precursor polypeptides to structural proteins of visna virus

Area of Science:

• Virology
• Molecular Biology
• Retrovirus Research

Background:

• Visna virus, a retrovirus, replicates in sheep choroid plexus cells.
• Virions contain internal proteins (p30, p16, p14), genomic RNA, reverse transcriptase, and an envelope glycoprotein (gp135).
• Structural proteins are likely encoded by gag, env, and pol genes.

Purpose of the Study:

• To elucidate the genetic organization and expression of the visna virus genome.
• To characterize the synthesis and precursors of viral proteins in infected cells.

Main Methods:

• Immunoprecipitation of pulse-labeled cell extracts using monospecific antisera against viral proteins.
• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for protein resolution.
• Tryptic peptide mapping to confirm precursor-product relationships.
• Pulse-chase experiments to study protein maturation.
• Use of 2-deoxy-d-glucose to accumulate non-glycosylated forms of env precursors.

Main Results:

• Identified a 55,000-dalton polypeptide precursor (Pr55(gag)) for internal virion proteins p30, p16, and p14.
• Confirmed Pr55(gag) as the precursor through tryptic peptide mapping.
• Detected a gag-related 150,000-dalton polypeptide (Pr150(gag-pol)), a likely precursor to reverse transcriptase.
• Characterized a glycosylated precursor (gPr150(env)) for gp135, with a non-glycosylated form of approximately 100,000 daltons.
• Visna virus possesses the largest non-glycosylated env-related precursor found in retroviruses.

Conclusions:

• Visna virus exhibits a complex protein synthesis pathway involving distinct precursors for gag, pol, and env genes.
• The large size of the env precursor suggests visna virus may have the largest env gene among retroviruses.
• These findings contribute to understanding retroviral genome organization and expression.