A single-stranded S1 nuclease hypersensitive site which contains a d(AT)(18) sequence structure located in the 5'-non transcription spacer of silkworm A. ricini ribosomal RNA gene has been reported([1]). Using starved-refed silkworms, another S1 nuclease sensitive site was found existing in the rDNA chromatin, while under merely starving, this S1 sensitive site disappeared([2]). Recently this inducible S1 sensitive site has been further determined. It consists of a d(GT)(10)-d(AT)(10) special DNA sequence at the transcription initiation region, and shows a behavior of ease in DNA-unwinding, indicating that S1 nuclease sensitive sites may have an important function in the regulation of rDNA transcription and replication.