CHANGES OF ENZYMES AND FACTORS INVOLVED IN DNA-SYNTHESIS DURING WHEATEMBRYO GERMINATION

We have previously purified and characterized wheat germ DNA polymeras es A and B. To determine the role played by DNA polymerases A and B in DNA replication, we have measured the level of their activities durin g wheat embryo germination. The level of cellular proteins known to be associated with DNA synthesis such as PCNA and DNA primase were also investigated. The activity of DNA polymerase A gradually increased rea ching a maximal level at 12 h after germination. Three days later, onl y a residual activity was detected. DNA polymerase B showed the same p attern during germination with very similar changes in activity. Our r esults indicate a striking correlation between maximal activities of D NA polymerase A, DNA polymerase B and optimal levels of DNA synthesis. These results support a replicative role of these enzymes. The activi ty of wheat DNA primase that copurifies with DNA polymerase A also inc reases during wheat germination. Taking together all its properties, a nd in spite of its behaviour with some inhibitors, DNA polymerase A ma y be considered as the plant counterpart of animal DNA polymerase ct. Concerning DNA polymerase B we have previously shown that PCNA stimula tes its processivity. Besides studying the changes of DNA polymerases A and B and DNA primase we have also studied changes in PCNA during ge rmination. We show that PCNA is present in wheat embryos at a constant relatively high level during the first 24 h of germination. After 48 h, the absence of PCNA is concomitant with an important decrease in DN A polymerase B activity. In this report we confirm the behaviour of DN A polymerase B as a delta-like activity.