UNUSUAL BIPHASIC MELTING BEHAVIOR OF RHODOTORULA-GRACILIS DNA

Ultraviolet, fluorescence and CD spectral analysis suggested unusual s tructural features of Rhodotorula gracilis ATCC 90950 DNA. R. gracilis DNA exhibited 13% hyperchromicity at 260 nm as against 26% shown by c alf thymus DNA. The biphasic melting curve, one phase between 88-92 de grees C and the other between 92-97 degrees C, was attributed to diffe rent unwinding pattern of R. gracilis a DNA as a function of rise in t emperature. The binding affinity of ethidium bromide to R. gracilis DN A determined was almost the same as that of calf thymus DNA. Fluoresce nce spectra with rise in temperature showed decrease in the quanta of fluorescence intensity after transition temperature, suggesting the qu enching due to variation in structure. The CD spectra of R. gracilis D NA did not resemble the spectra of any of the known DNA forms and it s howed increase in the magnitude of negative band with rise in temperat ure suggesting a B-C transition. Disruption of intramolecular and high er order structures by sonication and salt concentration did not chang e this behaviour implicating the influence of sequence and base compos ition of R. gracilis DNA on thermal melting transition. (C) 1995 Acade mic Press Inc.