Finding new human minisatellite sequences in the vicinity of long CA-rich sequences

Microsatellites and minisatellites are two classes of tandem repeat sequenc es differing in their size, mutation processes, and chromosomal distributio n. The boundary between the two classes is not defined. We have developed a convenient, hybridization-based human library screening procedure able to detect long CA-rich sequences. Analysis of cosmid clones derived from a chr omosome 1 library show that cross-hybridizing sequences tested are imperfec t CA-rich sequences, some of them showing a minisatellite organization. All but one of the 13 positive chromosome 1 clones studied are localized in ch romosomal bands to which minisatellites have previously been assigned, such as the 1pter cluster. To test the applicability of the procedure to minisa tellite detection on a larger scale, we then used a large-insert whole-geno me PAC library. Altogether, 22 new minisatellites have been identified in p ositive PAC and cosmid clones and 20 of them are telomeric. Among the 42 po sitive PAC clones localized within the human genome by FISH and/or linkage analysis, 25 (60%) are assigned to a terminal band of the karyotype, 4 (9%) are juxtacentromeric, and 13 (31%) are interstitial. The localization of a t least two of the interstitial PAC clones corresponds to previously charac terized minisatellite-containing regions and/or ancestrally telomeric bands , in agreement with this minisatellite-like distribution. The data obtained are in close agreement with the parallel investigation of human genome seq uence data and suggest that long human (CA)s are imperfect CA repeats belon ging to the minisatellite class of sequences. This approach provides a new tool to efficiently target genomic clones originating from subtelomeric dom ains, from which minisatellite sequences can readily be obtained.