Two yeast artificial chromosomes (YACs) spanning a total distance of 1.1 megabase pairs of DNA around the MCC (for mutated in colorectal carcinoma) and APC (for adenomatous polyposis coli) genes at 5q21 have been isolated and characterized. Starting from the MCC gene, a strategy was undertaken to identify constitutional submicroscopic deletions in familial adenomatous polyposis patients that might considerably narrow down the position of the APC gene. To this end, YACs identified by the MCC gene were screened across a chromosome 5-specific cosmid library to provide a source of DNA probes for genomic sanning. The cosmids isolated from these experiments were used to screen a panel of somatic cell hybrids containing chromosome 5 segregated from patients suspected to carry putative interstitial deletions. This screening approach led to the confirmation of a small heterozygous deletion in a polyposis patient that overlaps one of the two isolated YACs. This YAC has been shown to contain the entire APC gene, in addition to a significant portion of DNA flanking the 5' end of the gene, and should therefore prove a valuable resource for functional studies by transfer to colorectal tumorderived cell lines.Familial adenomatous polyposis (FAP) is an autosomal dominant predisposition to colorectal cancer, affecting about 1 in 5000 to 1 in 10,000 individuals in all populations studied (1).The corresponding gene, designated APC [for adenomatous polyposis coli (2)], was mapped to 5q21-q22 by linkage analysis (3, 4) following a cytogenetic report of a male patient with polyposis and an interstitial deletion on Sq (5). The high incidence of allele loss at 5q21-q22 in carcinomas of sporadic patients (6-9) suggests that APC mutations are common in sporadic colorectal adenocarcinomas.To clone the APC gene, our initial studies used two deletions similar to that originally identified by Herrera et al.(5) to localize probes to a region around the APC gene (10). Subsequently, landmark clones were derived by chromosomal microdissection and microcloning around 5q21-q22 (11,12). Clones that were localized within the two APC-related interstitial deletions were then used to isolate yeast artificial chromosomes (YACs) covering about 4 megabases (ref. 12; G.M.H. and J.R.T.J.W., unpublished results) in order to narrow the search for the APC gene among potential candidates.During this investigation, however, a candidate gene, MCC (for mutated in colorectal carcinoma), was identified by using a randomly isolated cosmid, L5.71, exhibiting a high frequency of allele loss (13) and which also identified a heterozygous 260-kilobase (kb) deletion in one polyposis family (14). After the discovery of MCC, Kinzler et al. (15) and Groden et al. (16) isolated the APC gene itself. In this paper we describe our approach to identifying the APC gene, which has led to the isolation of two overlapping YACs containing the MCC gene, one of which also includes the complete APC gene.
MATERIALS AND METHODS YACMethods. The YAC library used in these studies (17)...