DENATURED SUPERCOILED DNA - STRUCTURAL AND BIOLOGICAL-ACTIVITY

Supercoiled DNA on treatment with NaOH followed by neutralization prod uces a condensed structure (form I(d)). This structure does not split into topoisomers when run on long gel in presence of intercalating age nts and the migration of this form does not change appreciably in pres ence or absence of ethidium bromide. Relaxation of form I(d) by topois omerase I from pea chloroplast is facilitated more than form I. Single -stranded binding (SSB) protein binds more to form I(d) as evidenced f rom gel retardation study. Hydroxyl radical nicking is facilitiated in this form. Compared to form I, this form produces half the number of transformants, but adsorption and penetration remain almost same in bo th the forms. Post-transformational growth using P-32 labelled form I and form I(d) showed greater amount of degradation in form I(d).