Use of normal probability paper in determining thermal melting values of deoxyribonucleic acid

Abstract

A method is described of plotting deoxyribonucleic acid (DNA) thermal melting data which allows informat~on other than average content of guanine plus cytosine to be determined. Absorbancy ( A ) values, corrected for thermal expansion, are plotted on normal probability graph paper and the best straight line drawn. The 50 percentile point on the graph establ~shes the Tm value which allows calculation of the mean base composition. In addition the 2.a (twice the standard deviation) value is easily determined from the probability plot, thus providing information about the degree of variation from the mean in DNA base composition. Comparison of the probability plot and usual graphic methods of determining Tm values provided similar DNA composition data on 15 different strains of Streptococcus lactis, Streptococcus cremoris, and Streptococcus diacetilactis. When many A values obtained from streptococcal DNA samples showing skewed thermal melting curves ( S . lactis b and S. diacetilactis DRC-2) were plotted on normal probability paper, two intersecting straight lines were apparent on the graph. This suggested that there were two types of DNA in these organisms. Each had its own unimodal compositional distribution and its presence was confirmed by density gradient separation. The use of normal probability plots as a rapid method of determining average base composition of DNA samples is suggested. In addition, heterogeneity in base composition may be shown by this method of plotting the data.

Deoxyribonucleic Acid Hybridization Studies Among Some Strains of Group D and Group N Streptococci

“…These values are in agreement with those previously reported for these organisms (1 1, 22). The mean Tm for all strains of S. lactis was 83.6 * 0.4 (%C+C = 34.7 * 0.8); this value compares favorably with that of 83.9 reported by Knittel et al (18). S. faecium subsp.…”

Novel Properties of Satellite DNA from Muskmelon

“…3a for comparison. The use of normal probability plots can facilitate the analysis of melting curves of DNA containing more than one base-composition fraction (36). Such plots are shown in Fig.…”

Reassociation Kinetics and Cytophotometric Characterization of Peanut (Arachis hypogaea L.) DNA

“…The Tm of peanut taper. Use of normal probability paper facilitated rapid determi-DNA in this mixture was 60 C. The reassociation was carried out vation of the midpoints (Tm) of the hyperchromatic rise due to in a Shamadzu digital double-beam spectrophotometer model hermal denaturation (24). Calculation of base composition was UV-210A equipped with a water-jacketed sample compartment.…”