Difference in the expression level of DNA polymerase beta among mouse tissues: high expression in the pachytene spermatocyte.

The expression level of DNA polymerase beta was determined in various mouse tissues. Northern blot hybridization analysis using rat cDNA as a probe revealed that the mRNA of about 1.5 kb for this enzyme is present in all kinds of tissues examined, but its content widely varies among tissues; the most abundant DNA polymerase beta mRNA was present in the testis, which was followed by brain, thymus, and spleen. The mRNA content was low in heart, kidney, and liver. In testis and brain, two minor species of transcripts of 3.3 and 6.2 kb were detected in addition to that of 1.5 kb. DNA polymerase beta activities in these tissues were closely correlated with the mRNA content, indicating that the expression of this enzyme is mainly regulated by the level of the mRNA. A survey of DNA polymerase beta mRNA levels in the testes at successive postnatal developmental stages and in isolated spermatogenic cells indicated that DNA polymerase beta mRNA was most abundant in spermatocytes at early pachytene. Since meiotic recombination occurs in this period, DNA polymerase beta may be involved in the repair-type DNA synthesis associated with the recombination process.