Rapid assembly and disassembly of complementary DNA strands through an equilibrium intermediate state mediated by A1 hnRNP protein.

A1 hnRNP protein, which rapidly renatures complementary strands of nucleic acids in vitro, affects both the equilibrium and kinetic properties of the reaction (single-stranded DNA in equilibrium with double-stranded DNA). A1 lowers the melting transition of duplex DNA. However, at temperatures above this new Tm, both single- and double-stranded DNAs are present at equilibrium and are rapidly interconverting. Although the ratio of single and double strands under these conditions is a function of both the A1 protein and complementary DNA strand concentrations, it is not strongly affected by further increases in temperature. These surprising results demonstrate that A1 does not act as a simple catalyst in promoting renaturation and indicate how A1 and other proteins could act to speed the turnover of intermediate complexes in important biological processes.