STRUCTURAL AND MECHANISTIC RELATIONSHIPS BETWEEN NUCLEIC-ACID POLYMERASES

A superfamily of nucleic acid polymerases that includes the pol I and pol alpha classes of DNA-directed DNA polymerases, mitochondrial and p hage DNA-directed RNA polymerases, and most RNA-directed polymerases m ay be defined on the basis of the occurrence of conserved sequence mot ifs and tertiary structure similarities between HIV-1 reverse transcri ptase, DNA polymerase I and T7 RNA polymerase. Although sequence or st ructural similarities do not yet justify inclusion of the multi-subuni t DNA-directed RNA polymerases in this superfamily, mechanistic simila rities suggest a deep relationship between these and the simpler T7-li ke RNA polymerases.