No abstract

In the initial stages of influenza virus infection, the hemagglutinin (HA) protein of influenza virus mediates both adsorption and penetration of the virus into the host cell. Recently, we identified and characterized BMY-27709 as an inhibitor of the H1 and H2 subtypes of influenza A virus that specifically inhibits the HA function necessary for virus-cell membrane fusion(G.-X. Luo, R. Colonno, and M. Krystal, Virology 226:66-76, 1996). Studies presented herein show that the inhibition is mediated through specific interaction with the HA protein. This binding represses the low-pH-induced conformational change of the HA protein which is a prerequisite for membrane fusion. In an attempt to define the binding pocket within the HA molecule, a number of drug-resistant viruses have been isolated and characterized. Sequence analyses of the HA gene of these drug-resistant viruses mapped amino acid changes responsible for drug resistance to a region located near the amino terminus of HA2. In addition, we have identified inactive analogs of BMY-27709 which are able to compete out the inhibitory activity of BMY-27709. This finding suggests that inhibition of the HA-mediated membrane fusion by this class of compounds is not solely the result of binding within the HA molecule but requires specific interactions.

We previously purified a Crithidia fasciculata mitochondrial DNA polymerase that has unusual properties. Unlike a conventional mitochondrial DNA polymerase gamma, this enzyme is small, non-processive, deficient in 3'-exonuclease activity, and error prone (Torri, A. F., Kunkel, T. A., and Englund, P. T. (1994) J. Biol. Chem. 269, 8165-8171). In all of these characteristics, the enzyme resembles DNA polymerase beta, a nuclear enzyme thought to be involved in DNA repair. We have now cloned and sequenced the gene for this enzyme. The mitochondrial polymerase has significant homology, about 33% identity at the amino acid level, with human DNA polymerase beta. However, sequence analysis of the clone revealed the presence of a cleaved N-terminal presequence, presumably a mitochondrial import signal, which resembles presequences on other C. fasciculata mitochondrial proteins. The polymerase's function may be to repair the many gaps in newly replicated kinetoplast (mitochondrial) DNA minicircles in this parasite. This enzyme is the first example of a mitochondrial DNA polymerase beta.