Specific DNA-RNA hybrid recognition by TAL effectors.

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Transcription activator-like (TAL) effectors possess DNA-binding domains with tandem repeats.
• These TALE repeats form a superhelical structure that interacts with DNA duplexes.
• Previous studies focused on TAL effector interaction with DNA.

Purpose of the Study:

• To investigate the binding specificity of TALE repeats with DNA-RNA hybrids.
• To determine the structural basis of TALE repeat recognition of DNA-RNA hybrids.
• To explore the functional implications of this interaction, particularly concerning RNA stability.

Main Methods:

• X-ray crystallography to determine the structure of a designed TALE bound to a DNA-RNA hybrid.
• Biochemical assays to assess the accessibility of the RNA strand to RNases.
• Functional assays using an engineered TALE to evaluate protection against RNase H degradation.

Main Results:

• TALE repeats specifically recognize DNA-RNA hybrids, with binding specificity determined by the DNA strand.
• The crystal structure revealed TALE repeats in direct contact only with the DNA strand.
• The RNA strand's phosphodiester backbone was protected from RNase access.
• Engineered TAL effectors blocked RNase H degradation of an HIV-derived DNA-RNA hybrid.

Conclusions:

• TALE repeats can specifically bind DNA-RNA hybrids, expanding their known target interactions.
• The structural and functional data suggest a protective role for TALE binding against RNA degradation.
• This finding broadens the potential applications of TALE technology in DNA replication and retroviral infection processes.