Replication of each copy of the yeast 2 micron DNA plasmid occurs during the S phase

摘要: Abstract Saccharomyces cerevisiae contains 50–100 copies per cell of a circular plasmid called 2 micron DNA. Replication this DNA was studied in two ways. The distribution replication events among molecules examined by density transfer experiments with asynchronous cultures. data show that is similar to chromosomal replication: essentially all duplexes were hybrid at one doubling after the transfer, majority having fully dense strand and light strand. results occurs semiconservative mechanism where each replicates once cycle. only known example multiple-copy, extrachromosomal which every molecule Quantitative analysis indicates limited fraction period cycle when directly synchronous Synchronization accomplished sequentially arresting cells G1 phase using yeast pheromone α-factor incubating restrictive temperature for ( cdc 7 ) mutant. monitored adding 3 H-uracil previously labeled 14 C-uracil, determining 3H14C ratio purified species. did not occur during arrest periods. However, population doubled S permissive temperature, most occurring first third phase. Our indicate exists insures origin activated As DNA, further activation prevented until next We propose controls initiation identical