Spin labeled nucleic acids.

Area of Science:

• Biophysics
• Molecular Biology
• Biochemistry

Background:

• Spin labeling is a technique used to study the structure and dynamics of biological macromolecules.
• The electron spin resonance (ESR) signal of a spin label is sensitive to its local environment.

Purpose of the Study:

• To investigate how environmental factors like temperature and viscosity affect the ESR signals of spin labels attached to nucleic acids.
• To understand the relationship between nucleic acid structure, dynamics, and the observed ESR parameters.

Main Methods:

• Homopolyribonucleotides and E. coli DNA were spin labeled using an iodoacetamide-nitroxide compound.
• Spin-labeled nucleic acids were subjected to temperature and viscosity perturbations in aqueous solutions.
• Electron spin resonance (ESR) spectroscopy was used to analyze the signals and determine the correlation time (tau).

Main Results:

• The extent of spin labeling depended on the base composition and secondary structure of the nucleic acid.
• The spin label-polymer linkage showed instability at high temperatures and in phosphate buffers.
• Increasing temperature caused a linear decrease in the anisotropy factor of the ESR signal.
• The log(tau) versus 1/T profile was linear for single-stranded polynucleotides but showed discontinuities for duplexes at critical temperatures below the optical Tm.
• Increased viscosity linearly increased tau in aqueous sucrose solutions.

Conclusions:

• Environmental factors significantly influence the ESR signals of attached spin labels in nucleic acids.
• Temperature and viscosity perturbations provide insights into nucleic acid dynamics and structural transitions.
• The observed critical temperatures for duplexes suggest changes in their secondary structure.