AN INITIATION ZONE OF CHROMOSOMAL DNA-REPLICATION AT THE CHICKEN LYSOZYME GENE LOCUS

The chicken lysozyme gene domain is distinguished by a broad knowledge of how its expression is regulated. Here, we examined the in vivo rep lication of the lysozyme gene locus using polymerase chain reaction am plification and competitive polymerase chain reaction of size-fraction ated, nascent DNA strands. We found that DNA replication initiates at multiple sites within a broad initiation zone spanning at least 20 kil obases, which includes most of the lysozyme gene domain, The 5' border of this zone is probably located downstream of the lysozyme 5' nuclea r matrix attachment region. Preferred initiation occurs in a 3'-locate d subzone. The initiation zone at the lysozyme gene locus is also acti ve in nonexpressing Liver DU249 cells. Furthermore, examining the timi ng of DNA replication at the lysozyme gene locus revealed that the gen e locus replicates early during S phase in both HD11 and DU249 cells, irrespective of its transcriptional activity.