AGG repeats adopt several types of non-B DNA secondary structures, including triplex, tetra-duplex etc, which play important roles in gene transcription regulation and genome maintenance. By using an E.coli system, the propagation and repeats instabilities were studied. We found the repeats deletion instabilities and propagation instabilities were differently associated with repeats folding capacities in the leading and lagging strand template of a replication fork. Propagation instability was pronounced when AGG repeat was copied in the lagging strand template, of which the RecBCD pathway, .....