DNA replication is not restricted to specific regions in young vegetative Streptomyces mycelia

In order to determine the localization of DNA-synthesis in Streptomyces granaticolor and Streptomyces hygroscopicus, mycelia (growing either on agar or in liquid medium) were pulse-labelled with 3H-thymidine and prepared for autoradiography. The distribution of silver grains showed no regions of preferential incorporation of 3H-thymidine in mycelia up 300 micron in length. Since mycelia grow by apical elongation of hyphae, the frequency of silver grains was quantitatively analysed along individual main hyphase. No significant difference of labelling was found within zones of different age up to a distance of 80 micron from the hyphal tip. Also, the very youngest part of the hyphae enclosing only the most apically situated nucleoid did not show any deviation from the average frequency of silver grains.