Negative and positive mRNA splicing elements act competitively to regulate human immunodeficiency virus type 1 vif...

Area of Science:

• Molecular Biology
• Virology
• RNA Splicing

Background:

• Human immunodeficiency virus type 1 (HIV-1) produces over 40 mRNAs via alternative splicing.
• Regulation of HIV-1 splicing at 3' splice sites depends on suboptimal polypyrimidine tracts and cellular factors.
• Previous work showed optimizing the 5' splice site (5'ss) downstream of exon 2 (5'ss D2) increases splicing at 3'ss A1.

Purpose of the Study:

• To investigate the role of 5'ss D2 affinity for U1 snRNP in Vif expression.
• To identify other regulatory elements influencing HIV-1 exon 2 inclusion and Vif expression.

Main Methods:

• Mutagenesis of 5'ss D2 to alter U1 snRNP binding affinity.
• Analysis of mutations in the GGGG motif proximal to 5'ss D2.
• Identification and characterization of a novel exonic splicing enhancer (ESE) in exon 2.
• Investigation of SRp75 binding to the identified ESE.

Main Results:

• Mutations in 5'ss D2 altering U1 snRNP affinity modulated Vif expression.
• Mutations in the proximal GGGG motif increased exon 2 inclusion and Vif expression.
• A novel ESE in exon 2 was identified, binding SRp75 and enhancing exon inclusion and Vif expression.
• 5'ss D2 splicing was not essential for its effect on Vif expression.

Conclusions:

• HIV-1 Vif expression is regulated by a competitive interplay between 5'ss D2, the GGGG silencer, and an ESE.
• These regulatory elements collectively control vif mRNA splicing and accumulation.
• The findings suggest a mechanism for balancing vif mRNA and unspliced viral RNA levels for optimal HIV-1 replication.