Cloning and sequencing of a human 18S ribosomal RNA gene

A clone containing an 18S ribosomal RNA (rRNA) gene has been isolated from a human genomic library constructed in lambda Charon 4A. This gene was sequenced and found to be 1868 bp long. The sequence divergencies in the human 18S rRNA gene and the previously sequenced mouse and rat genes are found in one G + C-rich region of 110 bp located in the 5' domain of the molecule. Except for this variable region, extensive homology exists among these three mammalian genes. Overall, the human 18S rRNA gene is 98.8% homologous with those of rat and mouse.