Folding of an isolated ribonuclease H core fragment

Based on results from both equilibrium and kinetic hydrogen exchange studie s of Escherichia coli ribonuclease HI (RNase H), a fragment of RNase H (eAB CD) was designed. The sequence of eABCD contains less than half of the prot ein's primary sequence and includes the regions that were shown to be the m ost protected from hydrogen exchange in all previous studies of RNase H. Th is core fragment of RNase H encodes a well-ordered protein with native-like properties. When isolated from the full-length monomeric protein, the eABC D fragment forms a stable dimer. However, we show indirectly that the monom eric form of eABCD is folded and has an overall secondary structure similar to the dimeric form.