Human chromosomal centromere (AATGG)n sequence forms stable structures with unusual base pairs

Area of Science:

• Molecular Biology
• Biophysics
• Genetics

Background:

• Human centromeric satellite DNA, specifically the (AATGG)n (CCATT)n repeat, plays a crucial role in chromosome structure and function.
• Previous research indicated that the (AATGG)n sequence exists in an equilibrium between duplex and fold-back DNA structures.
• Understanding these DNA structures is vital for comprehending centromere organization and potential genetic instability.

Purpose of the Study:

• To elucidate the precise three-dimensional structure of human centromeric satellite DNA sequences.
• To investigate the structural dynamics and base-pairing characteristics within these repetitive DNA elements.
• To determine the impact of sequence motifs, such as the reverse (GGTAA) sequence, on DNA structural stability.

Main Methods:

• Utilized two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy to analyze nine DNA sequences.
• Employed NOE-constrained simulated annealing for structural refinement of d(CAATGG) and related sequences.
• Acquired 1D exchangeable proton NMR data to support structural models.

Main Results:

• Structural refinement revealed that the duplex form of the (AATGG)n sequence incorporates dynamic type-I Guanine-Adenine (G-A) base pairs.
• 1D exchangeable proton NMR data provided evidence supporting the presence of these dynamic G-A base pairs.
• The introduction of the reverse sequence motif (GGTAA) was found to destabilize the overall DNA structure.

Conclusions:

• The human centromeric satellite (AATGG)n sequence adopts a duplex DNA structure characterized by dynamic G-A base pairing.
• The stability of these centromeric DNA structures is sensitive to specific sequence arrangements, such as the reverse motif.
• These findings contribute to a deeper understanding of the structural basis of centromeric DNA and its potential implications in genome stability.