The identification of the Bs breakpoint and of two possible Bar genes.

Two coding regions were identified within a 110 kb region which includes all mapped Bar breakpoints. Both lie proximal to the identified Bar breakpoints. The first coding region, designated BarA, is 5 kb from the most proximal Bar mutation, B581, and 66 kb from the Bs breakpoint. It encodes a 1.3 kb transcript, which is found in late third instar larvae but is absent in 1-3-day-old pupae. Bi, R(B)hd3, B85c15, and Bs result in overproduction of this transcript in late third instar larvae. A second coding region, which was previously identified as BarH1, maps 18 kb from B581 and 79 kb from the Bs breakpoint. In third instar larvae, the abundance of the BarH1 transcript is very low in both wild type and various Bar mutatants, with the exception of R(B)hd3. In 1-3-day-old pupae, the level of the BarH1 transcript is higher. BarH1 was previously identified as the Bar gene. However, this report raises the possibility that BarA rather than BarH1 is the Bar gene or that more than one gene may be involved in Bar position effects.