Sikandar G. Khan, Thomas D. Schneider*, Kenneth H. Kraemer,
LMC and *LECB, NCIA poster to be presented at the 1998 NIH Research Festival October 6-9, 1998.
We studied 3 xeroderma pigmentosum (XP) group C (XPC) patients with multiple skin cancers and defective DNA repair. Amplification of the entire 3.5 kb XPC cDNA by RT-PCR showed an additional slowly migrating band with all 3 cell lines. Analysis of this band found an insertion of 83 nucleotides within exon 5. Sequencing the genomic DNA revealed a 1.5 kb intron (intron 5a) within exon 5 thereby splitting this region into exons 5a and 5b. The 83 bp insertion was found to be the 3' end of intron 5a and the splice acceptor sequence ended with "cag" in DNA from normal cells. We found single nucleotide changes: "Gag" in XP3BE, "cCg" in XP23BE, and "cGg" in XP24BE. These changes reduced the information content (Nucl. Acids Res. 25:4408-4415, 1997) of the intron 5a splice acceptor from 17.4 bits in the normal cells, to 11.5 bits, 10 bits and 9.3 bits, respectively and were associated with use of a cryptic alternative splice site 83 bases upstream in intron 5a. Only XP3BE also contained a mRNA species that skipped exon 5b. Two XP patients who are homozygous for this splice mutation have developed internal neoplasms (lung cancer and spinal cord astrocytoma).
origin: 1998 June 12
updated: 1998 June 12