Thermal Depolarization of Fluorescence From Polytene Chromosomes Stained With Acridine Orange

Abstract

The degree of polarization of fluorescence from stretched Chironomus thummi polytcne chromosomes, stained with low concentrations of acridine orange (AO), decreases with increasing temperature. The "half temperature" of this decrease (T1/2~) is lower than the expected DNA thermal denaturation temperature (Tin) by about 20°C. T1/2R is lowered as histone is removed from chromosomes. Balbiani ring regions of the fourth chromosome have T1/2R'S much lower than other regions, and nearly as low as chromosomes which had been extensively pretreated with trypsin to remove histone and other proteins. Measuremcnts of the thermal change in the rotational diffusion rate of AO in solution with DNA indicate that the temperature at which the DNA-AO bonding changes from a "rigid" to a "loose" mode varies with the GC percentage of the DNA, and in the same fashion as Tm, although 20°C lower.

Dna Organization in the Mature Sperm of Several Orthoptera by the Method of Polarized Fluorescence Microscopy

“…The polarized fluorescence microscope used in this study has been described in detail elsewhere (3). Basically, it consists of a fluorescence microscope with a rotating (20 rpm) polaroid situated above the ocular, and a photomultiplier tube above the polaroid to measure light intensities.…”

“…FIGURE3 A scan along the length of an A. domesticus mature sperm head of the intensity of fluorescent emission as the polaroid above the eyepiece rotates. The large oscillations indicate the cnsiderable polarization of the fluorescence.…”

The Orientation of Dna Within 80-Angstrom Chromatin Fibers

“…The methods and instrumentation used to measure fluorescence polarization in the microscope have been previously described (MacInnes and Uretz, 1967) . This instrument is basically a fluorescence microscope in which light from a selected area of the specimen can be passed through a rotating (6 rpm) dichroic filter to a photomultiplier tube .…”