--George Coupland, Christiane Plum and Peter Starlinger

We have shown that sequences internal to the 11bp inverted repeats are necessary for the transposition in Ac or Ds elements, even if the product of the Ac gene is provided in trans (MNL 62:46, 1988). We have extended these studies and have now seen that the internal sequences are not necessary for an all or none effect. A series of deletions extending from an internal position progressively towards the ends begins to decrease transposition frequencies at position 220 (marginally) and 195 (unmistakenly) from the 5'-end. No transposition is detected when the deletions extend to position 120 from the 5'-end. A deletion extending to position 170 shows an intermediate value. A similar pattern is seen at the 3'-end, where a decrease in transposition frequency is seen at position 170 from this end, while transposition is reduced to (near) zero, if the deletions extend to position 130 from the 3'-end. These results suggest that several functions (protein DNA interactions?) are necessary for optimal transposition. In connection with the results by R.Kunze et al. (see their report), the possibility arises that several molecules of the Ac gene product must bind simultaneously.

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