GENE CHARACTERIZATION, PROMOTER ANALYSIS, AND CHROMOSOMAL LOCALIZATION OF HUMAN BLEOMYCIN HYDROLASE

The human gene encoding bleomycin hydrolase, a cysteine proteinase inv olved in chemotherapy resistance, has been cloned, and its overall org anization has been established. The gene is composed of 12 coding exon s and 11 introns and spans more than 30 kilobases, The number and dist ribution of exons and introns differ from those reported for other hum an cysteine proteinases, indicating that these genes are only distantl y related. Nucleotide sequence analysis of about 1.2 kilobases of the 5'-flanking region of the human bleomycin hydrolase gene revealed a hi gh GC content, a ratio of CpG/GpC close to unity, and the absence of c onsensus transcriptional sequences such as TATA box or CCAAT box. All these features are characteristic of housekeeping genes and provide an explanation for the widespread expression of bleomycin hydrolase in h uman tissues. The B'-flanking region of the gene also contains a polym orphic CCG trinucleotide repeat that may be a target of genetic instab ility events and affect its transcriptional activity. Chromosomal loca lization of the human bleomycin hydrolase gene revealed that it maps t o chromosome 17q11.2, very close to the locus of the neurofibromatosis type 1 gene. This location is unique for any cysteine proteinase mapp ed to date. Finally, Southern blot analysis of DNA from leukocytes and autologous breast tumors has shown that the bleomycin hydrolase gene is not a frequent target of amplification in human breast carcinomas.