MAPPING OF A HUMAN RIBOSOMAL-RNA GENE IN THE YAC CONTIG SURROUNDING THE SMA CANDIDATE GENE

Using the yeast artificial chromosome (YAC) 116 flanking the autosomal recessive spinal muscular atrophy (SMA) gene region, we have screened a human fetal brain cDNA library and isolated the cDNA clone 14-3/9 w ith an insert size of 2.5 kb. The cDNA clone could be identified as pa rt of the human rRNA gene coding for 28S rRNA with a total size of 502 5 bp. The human 28S rRNA is involved in the organization of the 60S ri bosomal subparticle and is arranged in a 13-kb pre-rRNA transcription unit that occurs in tandem repeat clusters. Multiple copies of the rRN A gene have been mapped by pulsed field blot hybridization in the YAC contig between YAC 66 and YAC 116, which encompasses the SMA candidate gene, and additionally in the distally localized YAC 153.