R. Nagaraja et al., CHARACTERIZATION OF 4 HUMAN YAC LIBRARIES FOR CLONE SIZE, CHIMERISM AND X-CHROMOSOME SEQUENCE REPRESENTATION, Nucleic acids research, 22(16), 1994, pp. 3406-3411
Four collections of human X-specific YACs, derived from human cells co
ntaining supernumerary X chromosomes or from somatic cell hybrids cont
aining only X human DNA were characterized. In each collection, 80 - 8
5% of YAC strains contained a single X YAC. Five thousand YACs from th
e various libraries were sized, and cocloning was assessed in subsets
by the fraction of YAC insert-ends with non-X sequences. Cocloning was
substantial, ranging up to 50% for different collections; and in agre
ement with previous indications, in all libraries the larger the YACs,
the higher the level of cocloning. In libraries made from human - ham
ster hybrid cells, expected numbers of clones were recovered by STS-ba
sed screening; but unexpectedly, the two collections from cells with 4
or 5 X chromosomes yielded numbers of YACs corresponding to an appare
nt content of only about two X equivalents. Thus it is possible that t
he DNA of inactive X chromosomes is poorly cloned into YACs, speculati
vely perhaps because of its specialized chromatin structure.