Structure-function studies of nucleocytoplasmic transport of retroviral genomic RNA by mRNA export factor TAP

Area of Science:

• Molecular Biology
• Structural Biology
• Virology

Background:

• Messenger RNA (mRNA) export from the nucleus is crucial for gene expression.
• The TAP-p15 heterodimer functions as a key export receptor for cellular mRNA.
• Certain retroviruses utilize host cell machinery for their RNA export.

Purpose of the Study:

• To elucidate the structural basis of the interaction between the TAP-p15 heterodimer and simian type D retroviral constitutive transport element (CTE) RNA.
• To understand how CTE RNA hijacks the host mRNA export pathway for viral RNA nuclear export.

Main Methods:

• X-ray crystallography was used to determine the structure of the TAP protein's RNA recognition and leucine-rich repeat motifs bound to CTE RNA.
• Structure-guided mutations were introduced into TAP and CTE RNA.
• In vitro binding assays and in vivo transport assays were performed to assess the functional impact of mutations.

Main Results:

• The crystal structure revealed an L-shaped conformation for both TAP and CTE RNA, forming a mutual molecular embrace.
• Mutations affecting the protein-RNA interface significantly altered binding affinities and RNA export efficiency.
• The study identified specific molecular interactions governing the recognition of CTE RNA by TAP.

Conclusions:

• CTE RNA employs a specific structural motif to subvert the host mRNA export receptor TAP.
• This molecular mimicry facilitates the nuclear export of unspliced viral genomic RNAs.
• The findings provide general insights into how export receptors recognize and bind to cargo RNAs.