The CHD/Mi-2 proteins, which are characterised by the presence of two chromo (chromatin organization modifier) domains and an ATPase domain of the SWI/SNF class, have recently been shown to be integral components of a nucleosome remodeling and histone deacetylase complex (NuRD or Mi-2; Q-4). While the NuRD complex has been extensively described biochemically, little is known about the specific targets of the complex and the role that it plays in development. We have cloned and characterized the two C. elegans Mi-2 homologues, named chd-3 and chd-4. Phenotypic analysis of chd-3 and chd-4 mutant animals show that these genes have essential and partially redundant functions during development, including the repression of vulval cell fates (see accompanying abstract from VonZelewsky, Palladino et al.). To gain insight into the role of Mi-2 in development, we are carrying out a chd-4 suppressor screen. We will screen for extragenic suppressors which rescue the mid larval lethality associated with the chd-4 mutation. Amongst these suppressors could be loss of function mutations in downstream genes targeted by NuRD, or gain of function mutations of other downstream negative regulators of the target gene. Downstream targets may include regulators of growth control, proliferation and cell identity. Given that the let-60 ras pathway has been shown to interact with the NuRD complex in vulval development, the screen may also identify other members of this pathway. This might help establish the nature of the antagonism between the Rb and Ras pathways in both C. elegans and other organisms. We may also isolate additional components of the NuRD complex which interact directly with CHD-4. 1. Zhang, Y., et al., Cell, 1998. 95(2): p. 279-89. 2. Wade, P.A., et al., Curr Biol, 1998. 8(14): p. 843-6. 3. Tong, J.K., et al.,. Nature, 1998. 395(6705): p. 917-21. 4. Xue, Y., et al. Mol Cell, 1998. 2(6): p. 851-61. The CHD/Mi-2 proteins, which are characterised by the presence of two chromo (chromatin organization modifier) domains and an ATPase domain of the SWI/SNF class, have recently been shown to be integral components of a nucleosome remodeling and histone deacetylase complex (NuRD or Mi-2 complex; 1-4). While the Mi-2 complex has been extensively described biochemically, little is known about the specific targets of the complex and the role that it plays in development. We have cloned and characterized the two C. elegansMi-2 homologues, named chd-3 and chd-4. Phenotypic analysis of chd-3 and chd-4 mutant animals show that these genes have essential and partially redundant functions during development, including the repression of vulval cell fates (see accompanying abstract from VonZelewsky, Palladino et al.). To gain insight into the role of chd-4/Mi-2 in development, we are carrying out a chd-4 suppressor screen. We will screen for extragenic suppressors which rescue the mid larval lethality associated with the chd-4 mutation. Amongst these suppressors could be loss of function mutations in downstream genes targeted by the Mi-2-containing complex, or gain of function mutations of other downstream negative regulators of the target gene. Downstream targets may include regulators of growth control, proliferation , and cell identity. Given that the let-60 ras pathway has been shown to interact with a Mi-2- containing complex in vulval development, the screen may also identify other members of this pathway. This might help establish the nature of the antagonism between the Rb and Ras pathways in both C. elegans and other organisms. We may also isolate additional components of the Mi-2 containing complex which interact directly with CHD-4/Mi-2.