The 13p HSR in a human neuroblastoma cell line does not contain rRNA genes

We have studied a human neuroblastoma cell line containing a homogeneously staining region (HSR) on the short (p) arm of chromosome #13. The HSRs are believed to represent sites of gene amplification, containing multiple copies of one or a small number of genes. The 18S and 28S ribosomal RNA genes are the only structural genes so far assigned to the p arms of the human acrocentric chromosomes, which include number #13. Using two recombinant DNA probes specific for sequences in the 18S/28S ribosomal RNA (rRNA) gene complex for in situ hybridization, we have been able to establish that the 13pHSR in this line does not contain rRNA genes.