restriction maps , sequence data , and gene mapping studies demonstrate that ( i ) the rrna genes are transcribed in a telomere-to-centromere direction , ( ii ) the 5 ' end of the cluster and the adjacent non-rdna sequences are conserved on the five pairs of chromosomes , and ( iii ) the 5 ' end of the cluster is positioned about 3.7 kb upstream from the transcription initiation site of the first repeat unit .
C0085187
centromere
C0008633
chromosomes