General recombination in meiosis.

The meiotic events of homologous pairing and chiasma formation are apparently related to a number of meiotic processes. These include a delayed replication of small portion of genome (zygoDNA). L-protein, present transitionally in meiotic S-phase and leptotene, can bind to the specific sequences of zygo DNAs to form a nick and selectively suppress their replication until zygotene. Other meiosis specific proteins (R-protein, U-protein, rec A-like protein (m-rec) probably related with pairing and recombination but none of these, either alone or combination, is capable of inducing recombination in vitro. We have isolated proteins from meiotic and somatic cells that are capable of recombining two DNA plasmids in vitro. They have been designated m-recombinase and s-recombinase, respectively. m-recombinase appears during meiotic prophase with or without chiasma-formation, suggesting that regulation of meiotic recombination depends, not on the formation of appropriate enzymes but on rendering the enzymes effective by altering chromatin-structure. s-recombinase activity seems to be related to cell division and/or cell differentiation. The assay system used here for necessary recombination may be applicable to various situations.