THE DUAL EFFECT OF MIMOSINE ON DNA-REPLICATION

The plant amino acid, mimosine, is an extremely effective inhibitor of DNA replication in mammalian cells, but the mechanism by which this i nhibition is achieved is unknown. The drug has been proposed either to inhibit initiation at origins of replication or to inhibit chain elon gation by lowering nucleotide pool levels. In an attempt to determine which mode of action is correct, we have analyzed its effects on SV40 DNA replication. Using a two-dimensional gel replicon mapping techniqu e, we show that mimosine completely inhibits incorporation of [H-3]thy midine into viral DNA, but only after similar to 4 h. Qualitative anal ysis of replication intermediates during this interval suggests that t he drug partially inhibits both initiation and elongation, and pulse-c hase experiments support this contention. The drug has no effect when added directly to an SV40 in vitro replication extract. However, extra cts prepared from cells pretreated with mimosine are compromised in th eir ability to support replication in vitro in the presence of a full complement of nucleotides. Thus, although mimosine may alter nucleotid e pool levels in vivo, it also appears to affect one or more essential replication proteins. (C) 1997 Academic Press.