Summary Deletions of tumour-suppressor genes can be detected by loss of heterozygosity (LOH) studies, which were performed on 23 cases of adenocarcinoma of the oesophagus, using 120 microsatellite prmers coverng all non-acrocentric autosomal chromosome arms.The chromosomal arms most frequently demonstrating LOH were 3p (644% of tumours). 5q (45%), 9p (52%), lip (61%) Correspondence to: JK Field studies can lead to the identification of tumour-suppressor genes that are inactix ated in the metaplasia-dxsplasia-carcinoma progression. and may therefore be useful as biomarkers of future carcinogenesis in patients w-ith Barrett's metaplasia and dx splasia undergoing endoscopic surveillance. Previous alleleotype analx ses have detected LOH in more than 40%c of oesophageal adenocarcinomas on chromosome arms lp. 4q. 5q. 9p. 13q. 17p and 18q (Barrett et al. 1996a andHammoud et al. 1996). These allelotype studies AWere undertak-en Awith 43 and 39 microsatellite primers respectixely. We have performed the most comprehensive genomic study of oesophageal adenocarcinoma to date. coxering all of the non-acrocentnrc chromosome arms w-ith 120 microsatellite pnrmers. enabling identification of putatiVe tumour-suppressor gene sites in oesophageal adenocarcinoma. MATERIALS AND METHODS PatientsTwentv-three cases of adenocarcinoma of the oesophagus diagnosed betmeen 1992 and 1996 were studied. Twenty of these patients were male and their mean age xxas 68 y-ears. At present. six of these patients are alix e w ith no signs of recurrent disease. DNA extractionTissue from the tumour and from normal gastric mucosa were obtained from endoscopic biopsies and from surgical resections. snapped frozen in liquid nitroaen and stored at -70 C. Areas of tumour containincg minimal stromal cells wxere microdissected and DNA extracted from the microdissected tissues usinc the Nucleon II extraction kit (Scotlab).950

We have isolated several new clones of human ribosomal DNA. Each clone contains part of the external transcribed spacer, a complete 18 S-rRNA gene, the internal transcribed spacers, a complete 28 S-rRNA gene and a short downstream flanking region. We present a detailed map of the human ribosomal transcription unit with the locations of numerous useful restriction sites. In particular, a unique NheI site in the 5.8 S-rRNA gene enabled this gene to be mapped with respect to the 18 S-rRNA and 28 S-rRNA genes. The human 45 S-rRNA coding region is approx. 13,000 nucleotide residues long, of which the external transcribed spacer comprises approx. 3700 nucleotide residues and the first and second internal transcribed spacers comprise approx. 1070 and 1200 nucleotide residues respectively. A partial survey for sites of variation between clones has revealed a single point of variation among 18 S-rRNA gene sequences (a T/C variation at position 140), several sites of length variation in the regions of the transcribed spacers closely flanking the 18 S-rRNA genes, and some sites of length variation among 28 S-rRNA genes. Most of these sites of variation are associated with simple sequence tracts and are in regions that are known to undergo relatively rapid evolutionary divergence. In particular, the sites of variation among 28 S-rRNA genes occur in G + C-rich tracts whose lengths vary among vertebrates and that can be correlated with extensive hairpin structures previously observed by electron microscopy. Each of the clones so far surveyed in detail differs from the others in one or more respects.

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