Cloning and characterization of EagI YACs from human chromosome 21

Highly selective isolation of human DNAs from rodent-human hybrid cells as circular yeast artificial chromosomes by transformation-associated recombination cloning

Transformation-associated recombination (TAR) can be exploited in yeast to clone human DNAs. TAR cloning was previously accomplished using one or two telomere-containing vectors with a common human repeat(s) that could recombine with human DNA during transformation to generate yeast artificial chromosomes (YACs). On basis of the proposal that broken DNA ends are more recombinogenic than internal sequences, we have investigated if TAR cloning could be applied to the generation of circular YACs by using a single centromere vector containing various human repeats at opposite ends. Transformation with these vectors along with human DNA led to the efficient isolation of circular YACs with a mean size of approximately 150 kb. The circular YACs are stable and they can be easily separated from yeast chromosomes or moved into bacterial cells if the TAR vector contains an Escherichia coli F-factor cassette. More importantly, circular TAR cloning enabled the selective isolation of human DNAs from monochromosomal human-rodent hybrid cell lines. Although < 2% of the DNA in the hybrid cells was human, as much as 80% of transformants had human DNA YACs when a TAR cloning vector contained Alu repeats. The level of enrichment of human DNA was nearly 3000-fold. A comparable level of enrichment was demonstrated with DNA isolated from a radiation hybrid cell line containing only 5 Mb of human DNA. A high selectivity of human DNA cloning was also observed for linear TAR cloning with two telomere vectors. No human-rodent chimeras were detected among YACs generated by TAR cloning. The results with a circular TAR cloning vector or two vectors differed from results with a single-telomere vector in that the latter often resulted in a series of terminal deletions in linear YACs. This could provide a means for physical mapping of cloned material.

Repetitive sequence fingerprinting in the long range mapping of mammalian genomes

This review presents some properties of interspersed repeats, particularly human and mouse repeats, and shows how these have been utilized in long-range genome mapping. The link between the distribution of such repeats and their relationship with genome organization is discussed.

A human chromosome 7 yeast artificial chromosome (YAC) resource: construction, characterization, and screening

The paradigm of sequence-tagged site (STS)-content mapping involves the systematic assignment of STSs to individual cloned DNA segments. To date, yeast artificial chromosomes (YACs) represent the most commonly employed cloning system for constructing STS maps of large genomic intervals, such as whole human chromosomes. For developing a complete YAC-based STS-content map of human chromosome 7, we wished to utilize a limited set of YAC clones that were highly enriched for chromosome 7 DNA. Toward that end, we have assembled a human chromosome 7 YAC resource that consists of three major components: (1) a newly constructed library derived from a human-hamster hybrid cell line containing chromosome 7 as its only human DNA; (2) a chromosome 7-enriched sublibrary derived from the CEPH mega-YAC collection by Alu-polymerase chain reaction (Alu-PCR)-based hybridization; and (3) a set of YACs isolated from several total genomic libraries by screening for > 125 chromosome 7 STSs. In particular, the hybrid cell line-derived YACs, which comprise the majority of the clones in the resource, have a relatively low chimera frequency (10-20%) based on mapping isolated insert ends to panels of human-hamster hybrid cell lines and analyzing individual clones by fluorescence in situ hybridization. An efficient strategy for polymerase chain reaction (PCR)-based screening of this YAC resource, which totals 4190 clones, has been developed and utilized to identify corresponding YACs for > 600 STSs. The results of this initial screening effort indicate that the human chromosome 7 YAC resource provides an average of 6.9 positive clones per STS, a level of redundancy that should support the assembly of large YAC contigs and the construction of a high-resolution STS-content map of the chromosome.