Genomic clones of nm23-H1 and -H2 were isolated. The nm23-H1 and -H2 genes were located in a tandem array 4 kilobases apart. Each genome contained 5 exons and most of the splicing sites in the exon-intron junctions of two isotypes were essentially identical. A probe derived from intron 4 of nm23-H1 was used to examine the loss of heterozygosity (LOH) in primary colorectal carcinomas. Twenty-nine of 42 samples were informative and LOH was found in 3 of these 29. In all three samples with LOH, cancer tissue expressed lower levels of nm23-H1 mRNA when compared with those without LOH.


This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan.

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