RECOGNITION BY VIRAL AND CELLULAR DNA-POLYMERASES OF NUCLEOSIDES BEARING BASES WITH NONSTANDARD HYDROGEN-BONDING PATTERNS

The ability of DNA polymerases (pols) to catalyze the template-directe d synthesis of duplex oligonucleotides containing a nonstandard Watson -Crick base pair between a nucleotide bearing a 5-(2,4-diaminopyrimidi ne) heterocycle (d kappa) and a nucleotide bearing either deoxyxanthos ine (dX) or N-1-methyloxoformycin B (pi) has been investigated, The ka ppa-X and kappa-pi base pairs are joined by a hydrogen bonding pattern different from and exclusive of those joining the AT and GC base pair s, Reverse transcriptase from human immunodeficiency virus type 1 (HIV -1) incorporates dXTP into an oligonucleotide opposite d kappa in a te mplate with good fidelity, With lower efficiency and fidelity, HIV-1 r everse transcriptase also incorporates d kappa TP opposite dX in the t emplate, With d pi in the template, no incorporation of dKTP was obser ved with HIV reverse transcriptase, The Klenow fragment of DNA pol I f rom Escherichia coli does not incorporate d kappa TP opposite dX in a template but does incorporate dXTP opposite d kappa, Bovine DNA pols a lpha, beta, and epsilon accept neither dXTP opposite d kappa nor d kap pa TP opposite d pi. DNA pols alpha and epsilon (but not beta) incorpo rate d kappa TP opposite dX in a template but discontinue elongation a fter incorporating a single additional base, These results are discuss ed in light of the crystal structure for pol beta and general consider ations of how polymerases must interact with an incoming base pair to faithfully copy genetic information.