Nucleotide sequence of the transcription initiation region of a rat ribosomal RNA gene.

We cloned the part of the rDNA containing the transcription initiation region, and determined the exact site of initiation of the 45S RNA transcription. The nucleotide sequence of the region surround the initiation site was determined. Comparison of the mouse and rat genes revealed extensive homology between the initiation regions of the two species. Notably, upstream the transcription initiation site had higher homology (77%) than downstream (51%), suggesting functional significance of this region.