Studies on interaction between poly(L-lysine) and DNA of varied G + C contents

✍ Scribed by Hsueh Jei Li; Louis Herlands; Regina Santella; Paul Epstein

• Publisher: Wiley (John Wiley & Sons)
• Year: 1975
• Tongue: English
• Weight: 752 KB
• Volume: 14
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1975.360141113

✦ Synopsis

Interaction between polylysine and DNA's of varied G + C contents was studied using thermal denaturation and circular dichroism (CD). For each complex there is one melting band at a lower temperature t,,, corresponding to the helix-coil transition of free base pairs, and another band a t a higher temperature t', , corresponding to the transition of polylysine-bound base pairs. For free base pairs, with natural DNA's and poly(dA-dT) a linear relation is observed between the t , and the G + C content of the particular DNA used. This is not true with poly(dG).poly(dC), which has a t,, about 20°C lower than the extrapolated value for DNA of 10Ooh G + C. For polylysine-bound base pairs, a linear relation is also observed between the t'", and the G + C content of natural DNA's but neither poly(dA-dT) nor poly(dG).poly(dC) complexes follow this relationship. The dependence of melting temperature on composition, expressed as dt,ldX(:.c, where X(;.C. is the fraction of G-C pairs, is 60°C for free base pairs and only 21OC for polylysine-bound base pairs. This reduction in compositional dependence of T,,, is similar to that observed for pure DNA in high ionic strength. Although the t', of polylysine-poly(dA-dT) is 9°C lower than the extrapolated value for 0% G + C in EDTA buffer, i t is independent of ionic strength in the medium and is equal to the t,O extrapolated from the linear plot of t , against log Na+. There is also a noticeable similarity in the CD spectra of polylysine. and polyarginine.DNA complexes, except for complexes with poly(dA-dT). The calculated CD spectrum of polylysine-bound poly(dA-dT) is substantially different from that of polyarginine-bound poly(dA-dT).