Supercoiling unwinds two-micrometer plasmid yeast DNA at the origin of replication.
Stoynov SS, Dolapchiev LB
International Journal of Biochemistry & Cell Biology (2001)
Category: topoisomerase ¤ Added: Nov 19, 2002 ¤ Rating: ◊◊
All studied origins of replication of DNA in Saccharomyces cere6isiae contain DNA unwinding elements. The introduction of unrestrained negative supercoiling leads to melting of the two DNA strands in DNA unwinding elements. To understand the mechanism of DNA replication it is important to know whether the most unstable region of DNA coincides with the origin of replication. Two-micrometer plasmid DNA from S. cere6isiae inserted in pBR322 was investigated by cleaving with snake venom phosphodiesterase. Its single-strand endonucleolytic activity allows cutting of negatively supercoiled DNA in the DNA unwinding elements. The sites of the venom phosphodiesterase hydrolysis were mapped by restriction enzymes. This study shows that the unwinding of the two-micrometers plasmid DNA of S. cere6isiae takes place only in the origin of replication as a result of unrestrained negative supercoiling.