We used a combination of sequence analysis and exon trapping in an effort to determine the complete transcript map for a cosmid (6E5) derived from 12q13.3, a region of DNA sequence amplification in human cancers. This cosmid, previously known to contain three genes (CDK4, SAS, and OS9), was sequenced, and that information was used for computer-assisted analysis. In addition, 6E5 was subjected to both internal and 3'-terminal exon-trapping protocols, and the results of these studies were used to guide cDNA cloning experiments. These studies demonstrate that this cosmid is derived from a remarkably gene-dense region and add two new transcripts (KIAA0167 and 6E5.2) to the list of sequences that are expressed in tumors bearing amplification of this region.