Abstract
The present study deals with the determination whether or not the incorporation of base analogues into DNA occurs in the early instar larvae of silkworm, Bombyx mori. When the larvae are administered with 5-bromouracil (BU) containing BU-2-14C through the first and the second instar, a radioactive DNA and its hydrolysate with some of the properties of BU could be isolated from the larvae just after the second ecdysis. From cytological and autoradiographical observations using 5-bromodeoxyuridine (BUdR)-6-3H, the incorporation of BUdR into the nuclei was restricted within their DNA synthetic period in various tissues. It is speculated that when larvae are administered with BUdR at its various stages during the first instar, the change in mortarity is in parallel with the incorporation of BUdR into the nuclei of almost all the tissues, and that the same type of parallelism was true between changes in the frequency of the production of aberrant spots and of BUdR incorporation into the nuclei of epidermis which is considered a critical tissue.
