Stereochemical control of DNA biosynthesis

Stereochemical control of DNA biosynthesis was studied using several DNA-sy nthesizing complexes containing, in each case, a single substitution of a 2 '-deoxy-D-nucleotide residue by an enantiomeric L-nucleotide residue in a D NA chain (either in the primer or in the template) as well as 5'-deoxy-L-ri bonucleoside 5'-triphosphates (L-dNTPs) as substrates. Three template-depen dent DNA polymerases were tested, Escherichia coli DNA polymerase I Klenow fragment, Thermus aquaticus DNA polymerase and avian myeloblastosis virus r everse transcriptase, as well as template-independent calf-thymus terminal deoxynucleotidyl transferase. Very stringent control of stereoselectivity w as demonstrated for template-dependent DNA polymerases, whereas terminal de oxynucleotidyl transferase was less selective. DNA polymerase I and reverse transcriptase catalyzed formation of dinucleoside 5',5'-tetraphosphates wh en L-dTTP was used as substrate. Comparison between models of template-prim er complexes, modified or not by a single L-nucleotide residue, revealed st riking differences in their geometry.