Further proof was obtained for the actual incorporation of DNA polymerase I into a complex of higher molecular weight which unlike the free polymerase, is active with native DNA templates. It was shown that the loss of 5' through 3' exonuclease from DNA polymerase I renders the molecule less hydrophobic as well as making it incompetent for complex formation. This plus the genetic evidence which shows that the 5' through 3' exonuclease is required for cell viability plus the fact that a factor "E", essential for complex formation and stability, is associated with the membranes suggests that complex may perform some essential function at the cell membrane surface.