VACCINIA VIRUS-DNA TOPOISOMERASE-I PREFERENTIALLY REMOVES POSITIVE SUPERCOILS FROM DNA

Type I DNA topoisomerases homologous to Escherichia coli topoisomerase I normally only remove negative supercoils from DNA. Topoisomerases I from various eukaryotes share sequence homology and remove both posit ive and negative supercoils from DNA. Here we report that vaccinia vir us topoisomerase I has significant difference in substrate preference from the other homologous type I topoisomerases. Vaccinia virus topois omerase I shows a definite preference for removal of positive supercoi ls. In contrast, topoisomerase I from human, wheat germ and Saccharomy ces cerevisiae has little preference between positive and negative sup ercoils. The vaccinia enzyme may have evolved for functions required f or optimal viral growth.