Mini-chromosomes derived from the human Y chromosome by telomere directed chromosome breakage.

We have used telomeric DNA to break two acrocentric derivatives of the human Y chromosome into mini-chromosomes that are small enough to be size- fractionated by pulsed-field gel electrophoresis. One of the mini-chromosomes is about 7 Mb in size and sequence-tagged site analysis of this molecule suggests that it corresponds to a simple truncation of the short arm of the Y chromosome. Five of the mini-chromosomes are derived from the long arm, are all rearranged by more than a simple truncation, and range in size from 4.0 Mb to 9 Mb. We have studied the mitotic stabilities of these mini-chromosomes and shown that they are stably maintained by cells proliferating in culture for about 100 cell divisions.

Molecular cloning of a rat chromosome putative recombinogenic sequence homologous to the hepatitis B virus encapsidation signal.

Previously, we reported that a 61-bp subgenomic HBV DNA sequence (designated as 15AB, nt 1855-1915) is a hot spot for genomic recombination and that a cellular protein binding to 15AB may be the putative recombinogenic protein. In the present study, we established the existence of a 15AB-like sequence in human and rat chromosomal DNA by Southern blot analysis. The 15AB-like sequence isolated from the rat chromosome demonstrated a 80.9% identity with 5'-CCAAGCTGTGCCTTGGGTGGC-3', at 1872-1892 of the hepatitis B virus genome, thought to be the essential region for recombination. Interestingly, this 15AB-like sequence also contained the pentanucleotide motifs GCTGG and CCAGC as an inverted repeat, part of the chi known hot spot for recombination in Escherichia coli. Importantly, a portion of the 15AB-like sequence is homologous (82.1%, 23/28 bp) to break point clusters of the human promyelocytic leukemia (PML) gene, characterized by a translocation [t(15;17)], and to rearranged mouse DNA for the immunoglobulin kappa light chain. Moreover, 15AB and 15AB-like sequences have striking homologies (12/15 = 80.0% and 13/15 = 86.7%, respectively) to the consensus sequence for topoisomerase II. Our present results suggest that this 15AB-like sequence in the rat genome might be a recombinogenic candidate triggering genomic instability in carcinogenesis.