A selective DNA polymerase inhibitor recovered from sera and cells of tumor bearing mice
Description
The existence of an unusual DNA polymerase, the R1 polymerase, obtainable from MOPC-21 mouse myeloma tissue has been previously shown by Gottlieb and co-workers. It has been further shown that this enzyme and the (gamma) DNA Polymerase were inhibited by a DNA species present in the sera of mice bearing certain malignancies including the MOPC-21 myeloma but not present in sera of normal mice. This inhibition was specific in that other DNA polymerases tested, including the Rauscher murine leukemia virus (RMLV) polymerase, were not inhibited to as great an extent as the R1 and (gamma) DNA polymerases. The inhibitor DNA could be purified from serum as well as from MOPC-21 mouse myeloma tissue and was estimated to have a size of about 180 base pairs In work described here, it was determined that the inhibitor DNA was present in normal BALB/c liver tissue, but was obtained with a yield of only 15% of that from MOPC-21 myeloma. Inhibitor DNA from MOPC-21 myeloma and from BALB/c liver were cloned into the phage M13mp8. Agarose gel electrophoresis and DNA sequencing showed the cloned liver inhibitor inserts to be somewhat shorter than the MOPC-21 inserts. Inhibitor DNA was found not to be homogeneous in sequence. All inserts tested from both sources inhibited the R1 polymerase to a greater extent than the RMLV polymerase and were of a size close to that estimated for inhibitor from serum and tumor. This showed that the cloned inhibitor retained the characteristics of the preparations from which it was cloned. A 180 base pair DNA fragment from M13mp8 gave less inhibition of the R1 enzyme than did any of the cloned inhibitor inserts suggesting that the inhibition was sequence specific