FIG. 4.
Irregular transposon circle junctions caused by mutations M20-21 to M24-25. Four parallel experiments were carried out with each mutant to isolate transposon circles containing the IR-IR junction. The isolated DNA samples were transformed into TG2 cells, and plasmid DNA was purified from all the Cms colonies (if any) from each parallel experiment and analyzed by PvuII (Pv) digestion. One circle junction not cleavable by PvuII was sequenced from each experiment. Transposons harboring M20-21, M22-23, or M24-25 in both IRs consistently resulted in aberrant spacers of 1 or 3 bp. For M20-21, the four parallel experiments yielded four different irregular junctions and M22-23 bore three independent Cms derivatives, of which two contained identical junctions and one carried a small deletion (data not shown), while M24-25 produced only two independent Cms derivatives with different spacers. Uppercase letters, the first and last two nucleotides of the IS30 ends; lowercase letters, the flanking sequence in the donor plasmid or the spacer sequence detected by sequencing. Other symbols are as defined in the legend to Fig. 1.