mtDNA polymerase, commonly termed DNA polymerase-y, has been studied sporadically over the years, but only recently has information become available on its actual size and some of its functional features. There are several reports of an associated 3 +5 exonuclease activity being an intrinsic part of the polymerase; it likely confers a proofreading capacity consistent with studies on the error rate of DNA polymerase-y Kaguni and 01-son 1989 [for Drosophila melanogaster]). The catalytic subunit of the holoenzyme appears to be of significant size, approximately 140 kD in Xenopus laevis a similar situation may prevail for D. melanogaster in both these