Magnetic circular dichroism study on synthetic polynucleotides, bacteriophage structure, and DNA's

✍ Scribed by Marcos F. Maestre; Donald M. Gray; Randall B. Cook

• Publisher: Wiley (John Wiley & Sons)
• Year: 1971
• Tongue: English
• Weight: 884 KB
• Volume: 10
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360101214

✦ Synopsis

The MCD (magnetic circular dichroism) spectra of Ap, ApA, ApApA, poly A, Up, UpU, poly U and double-stranded poly A:U alternating copoly A-U and alternating deoxyribopoly A-T were measured with a Cary 61 spectropolarimeter fitted with a Varian superconducting magnet at, a field strengt,h of 50 Kgauss. The hlC1) spectra of T 2 and T.5 DNA at various stages of heat denatnration were measured as a funct.ion of hyperchromicity of the sample. RICD spectra of the intact and degraded T2 and T.5 phages were used to study the degree of alteration of t.he IINA inside the phages versus the DNA in vi/ro. The results for the adenine polymers show that the main MCI) bands, B,. (271 rim), B1, (232 nm), and El. (212 nm), show a decrease ill specific magnitude as the length of the polymer is increased, reflecting the degree of stacking of t,he polymer. In contrast, the uridine series of polymers shows little change of the MCD bands, indicating that there is little interaction between the bases regardless of i.he length of the polymers. The MCII spectra of poly A:U, alternat,ing poly r(A-U): (A-U), and alternating poly d(A-T): (A-T) show significant differences among themselves in the magnitude of the B,, band and when compared with the sum of the spectrum for the poly A plus poly U. This may indicate the selective effect of hydrogen bonding on the B,, band. Alternatively, the difference may be due to the absence of an TL + T* transition in the donble-stranded polymer. Measurements of denatured T2 and T.5 DXA's show increases in all AICI) bands. The T2 DNA internally packed in phage shows an increase of the B," and E l , bands, the B1, remaining unchanged. The int.ernal T,j DNA shows an increase of t.he B1, band only. Thus, the internal DNA structure is altered in a manner quite different from a simple denatnration caused by hydrogen bond breaking. Furthermore, different 11CD bands indicate that different modes of DNA packing exist, for T2 and T5 phages.