XXXX reverse transcriptase and ribonuclease H as substrates of the viral protease.

@entity2858 @entity9288 @entity4206 @entity4022 @entity645 @entity19490 @entity815 @entity1473
A study has been made of the susceptibility of recombinant constructs of reverse transcriptase (RT) and ribonuclease H (RNase H) from @entity2858 ) to digestion by the @entity2858 protease. At neutral pH, the protease attacks a single peptide bond, @entity815 440-Tyr441, in one of the protomers of the folded, active RT/RNase H ( @entity19490 / @entity19490 ) homodimer to give a stable, active heterodimer ( @entity19490 / @entity4206 ) that is resistant to further hydrolysis (Chattopadhyay, D., et al., 1992, J. Biol. Chem. 267, 14227-14232). The @entity1473 -terminal @entity9288 fragment released in the process, however, is rapidly degraded by the protease by cleavage at Tyr483-Leu484 and Tyr532-Leu533. In marked contrast to this @entity9288 segment, both @entity19490 / @entity4206 and a folded RNase H construct are stable to breakdown by the protease at neutral pH. It is only at pH values around 4 that these latter proteins appear to unfold and, under these conditions, the heterodimer undergoes extensive proteolysis. RNase H is also hydrolyzed at low pH, but cleavage takes place primarily at @entity4022 436-Ala437 and at @entity815 440-Tyr441, and only much more slowly at residues 483, 494, and 532. This observation can be reconciled by inspection of crystallographic models of RNase H, which show that residues 483, 494, and 532 are relatively inaccessible in comparison to @entity4022 436 and @entity815 440. Our results fit a model in which the @entity19490 / @entity19490 homodimer exists in a conformation that mirrors that of the heterodimer, but with a @entity9288 segment on one of the protomers that is structurally disordered to the extent that all of its potential @entity645 protease cleavage sites are accessible for hydrolysis.
