New 5'-(CGG)n-3' repeats in the human genome.

We identified new, potentially unstable loci in the human genome containing 5'-(CGG)n-3' trinucleotide repeats by screening a human subgenomic library as well as a chromosome 16 library with a 5'-(CGG)17-3' oligodeoxyribonucleotide probe. Five different clones were isolated, two from the chromosome 16 library and three from the subgenomic library. Determinations of the nucleotide sequences have revealed that the E7 clone displayed, in addition to the 5'-(CGG)n-3' trinucleotide repeat, a 5'-(CAG)n-3' and a 5'-(CCT)n-3' trinucleotide repeat. Two clones, CL16-1 and P5-5, had homologies to known genes, the human casein kinase II alpha' subunit (chromosome 16) and the human calcium-activated potassium channel (chromosome 10), respectively. Clones E7 and P4 were assigned to chromosome 6, whereas CL16-8 mapped to chromosome 16. Their potential coding capacities were assessed by RNA transfer (Northern blotting) experiments. Four different transcripts were identified by using the E7 clones as hybridization probes, three of them being brain-specific. The P4 clone was expressed in placenta and skeletal muscle. Minor polymorphisms within the repeats were observed in normal and in fragile X individuals. Lung and colon carcinoma cell lines in which some microsatellites were shown to be unstable were also investigated. Expansions of the 5'-(CGG)n-3' repeats were not found.