ANALYSIS OF CFTR TRANSCRIPTS IN NASAL EPITHELIAL-CELLS AND LYMPHOBLASTS OF A CYSTIC-FIBROSIS PATIENT WITH 621-]T AND 711+1G-]T MUTATIONS(1G)

We have analyzed the CFTR mRNA populations in a cystic fibrosis patien t heterozygous for the 621+1G-->T and 711+1G-->T mutations. Total RNA isolated from the nasal epithelial cells and Epstein-Barr virus-transf ormed lymphoblasts derived from this patient was reversely transcribed and a region extending from exon 3 to exon 7 of the gene was amplifie d by the polymerase chain reaction and analyzed. Three abnormal produc ts were identified, suggesting the presence of three aberrant transcri pts, and their profiles were identical in both cell types. Two of the products were found to be missing either exon 4 or exon 5 as anticipat ed from the transcripts from the 621+1G-->T or 711+1G-->T alleles, res pectively. The third product was apparently derived from an alternativ ely spliced mRNA species in the absence of the nominal splice site (in 621+1G-->T) through the use of a cryptic splice donor sequence (TT528 /GTGAGG) within exon 4. Although reading frames appeared to be preserv ed in all three putative transcripts, significant portions of the pres umed first and second transmembrane spans as well as the immediately f ollowing cytoplasmic domain would be deleted from the mutant CFTR poly peptides, if made. These observations are consistent with a loss of CF TR function in this cystic fibrosis patient.