lin-35 and lin-53, two genes that antagonize a C-elegans Ras pathway, encode proteins similar to Rb and its binding protein RbAp48

The Ras signaling pathway for vulval induction in Caenorhabditis elegans is antagonized by the activity of the synthetic multivulva (synMuv) genes, wh ich define two functionally redundant pathways. We have characterized two g enes in one of these pathways. lin-35 encodes a protein similar to the tumo r suppressor Rb and the closely related proteins p107 and p130. lin-53 enco des a protein similar to RbAp48, a mammalian protein that binds Rb. In mamm als, Rb and related proteins act as regulators of E2F transcription factors , and RbAp48 may act with such proteins as a transcriptional corepressor. W e propose that LIN-35 and LIN-53 antagonize the Ras signaling pathway in C. elegans by repressing transcription in the vulval precursor cells of genes required for the expression of vulval cell fates.