Point mutations change the thermal denaturation profile of a short DNA fragment containing the lactose control elements. Comparison between experiment and theory
Schaeffer, F.; Kolb, A.; Buc, H.
EMBO Journal 1(1): 99-105
1982
ISSN/ISBN: 0261-4189 PMID: 7188180 Document Number: 196362
To understand the denaturation process of short DNA segments, a 203 base pair (bp) (Escherichia coli) restriction fragment containing the lactose control region. A steady decrease in GC (guanine-cytosine)content exists between its i proximal and z proximal ends. This fragments melts at low salt in 2 subtransitions. A GC to AT(adenine-thymine) mutation in the AT-rich region (mutation UV5) increases the number of denatured base pairs in the 1st subtransition and decreases the cooperativity of the melting process. A GC to AT mutation in the GC-rich region (mutation L8) decreases the number of denatured base pairs in the 1st subtransition and increases the cooperativity. These mutations induce the same shift in the temperature of half denaturation. The effects of both mutations are additive. A short deletion at the z end of the fragment affects only the 1st subtransition. When 4 GC pairs are added to both ends, the fragment melts in 1 transition. Comparison with the results obtained with a larger 789 bp lac fragment reveals strong end effects on base pair stability and suggests that denaturation of the 203 bp fragment proceeds unidirectionally from the z end. Good agreement is shown with the predictions made with the "zipper model" of Crothers et al (1965).