Initiation of DNA replication at the Chinese hamster origin oriGNAI3 relies on local sequences and/or chromatin structures, but not on transcription of the nearby GNAI3 gene

We recently identified a region of preferential replication initiation, ori GNAI3, near the 3' end of the Chinese hamster GNAI3 gene. oriGNAI3 is co-am plified in mutants selected for AMPD2 amplification, a process generating c hromosomal rearrangements. In this report we have taken advantage of cell l ines with truncated and translocated amplified units to show that these rea rrangements do not alter the function of oriGNAI3. These results indicate t hat replication initiation at this locus relies essentially on local featur es. Interestingly, the study of one line in which a rearrangement has disru pted the GNAI3 gene shows that ongoing transcription of this gene is not re quired for initiation at oriGNAI3. In order to obtain further insight into the sequences and/or chromatin structures required for oriGNAI3 function, w e have analyzed the DNase I sensitivity and nucleotide sequence of the regi on. The features important for replication initiation appear to cluster in a 7-12 kb region which includes oriGNAI3.