In the Bar mutation of Drosophila, ommatidial differentiation is known to be suppressed in the anterior portion of the eye. Our structural analysis shows that the Bar region contains a pair of homeo box genes, BarHl and BarHZ. These genes encode polypeptides similar in size and sequence and share a common homeo domain that is identical in sequence except for putative trflns-activator-binding sites. We also show, by mosaic analysis and immunostaining with anti-BarHl/BarH2 antibodies, that BarHl and BarHZ are not only specifically coexpressed but also functionally required in R1/R6 prephotoreceptors and primary pigment cells in developing ommatidia. In R1/R6, the expression of BarHl and BarHZ appears to be regulated by rough and glass gene products. BarHl and BarHZ proteins are essential to normal lens formation, formation of three types of pigment cells, and elimination of excess cells from mature ommatidia. Taken together, our results suggest that Bar homeo domain proteins may play key roles in the fate-determination processes of pigment cells and cone cells.

We have cloned a novel regulator protein, p122, in the PLC‐delta signalling pathway by screening a rat brain expression library with antiserum raised against purified phospholipase C‐delta 1 (PLC‐delta 1). This novel p122‐RhoGAP binds to PLC‐delta 1 and activates the phosphatidylinositol 4,5‐bisphosphate (PIP2) hydrolyzing activity of PLC‐delta 1. As suggested by the deduced amino acid sequence, this regulator protein shows a similarity to the GTPase activating protein (GAP) homology region of Bcr and possesses GAP activity for RhoA, but not for Rac1; no guanine nucleotide exchange activity for RhoA and Rac1 was detected. These findings suggest that this novel RhoGAP is involved in the Rho signalling pathway, probably downstream of Rho activation, and mediates the stimulation of PLC‐delta, which leads to actin‐related cytoskeletal changes through the hydrolysis of PIP2, which binds to actin binding proteins such as gelsolin and profilin.

Calcium-dependent protease (calcium protease) is apparently involved in a variety of cellular processes. Here we have attempted to clarify the role and regulatory mechanism of calcium protease by analysing its structure. The complete primary structure of calcium protease (relative molecular mass (Mr) 80,000 (80K), 705 amino acids) was deduced from the nucleotide sequence of cloned complementary DNA. The protein contains four distinct domains, and we have observed a marked similarity between the second and fourth domains and the papain-like thiol proteases and calmodulin-like calcium-binding proteins, respectively. This finding suggests that calcium protease arose from the fusion of genes for proteins of completely different function and evolutionary origin. Further, it provides functional insight into cellular regulatory mechanisms mediated by Ca2+ through calcium-binding proteins.

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