DNA- and RNA-Dependent DNA Polymerases: Progressive Changes in Rabbit Endometrium During Preimplantation Stage of Pregnancy1

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Abstract
DNA polymerase activities were studied in rabbit endometria at estrus and through the first 7 days of pregnancy. Extracts of total endometrial homogenates by high salt gave 2 peaks of polymerase activity by sucrose gradient centrifugation; the 6-8S polymerase showed considerable increase in specific activity which reached a maximum at 5-7 days post-coitum but the 3-4S polymerase showed only a slight increase after 2 days of pregnancy. A 5-6S RNA-dependent DNA polymerase activity, extracted by combined use of hypertonic salt solution and non-ionic detergent from particulate subcellular functions, appeared in the endometrium after coitus, reached a maximum at day 3-4 and declined thereafter. This RNA-dependent DNA polymerase activity, isolated by phosphocellulose chromatography at distinct regions of salt gradient, showed preference for template-primers such as (rA)n.cntdot.(dT)9 and (rC)n.cntdot.(dG)6 but did not utilize 70S RNA of RNA tumor viruses. Attempts to demonstrate oncorna virus expression by other means have been unsuccessful with endometrium of 3 day pregnant rabbits. Interrelation between the changes of these DNA polymerase activities and the DNA replication in the endometrial cells is discussed.

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