Fig. 2. (A) Two transcripts, lin-40a and lin-40b, are generated from the lin-40 locus by alternative splicing. cDNA clones that represent both transcripts have a polyA tail at their 3' ends and an in-frame stop codon in front of the start codon. Arrows on top of the genomic sequence and protein products in B indicate the positions of mutations in lin-40 alleles. (B) The protein structure of MTA1 proteins. Human MTA1 (hMTA-1) and its homologues in C. elegans, LIN-40A, LIN-40B and EGL-27, share some consensus peptide motifs, including a leucine zipper, a SANT domain and a zinc-finger motif. The SH3-binding domain is only present in mammalian MTA1. The hatched domain in LIN-40B represents the sequence that interacts with LIN-36 and LIN-53 in a two-hybrid screen. (C,D) The expression pattern of a lin-40a::gfp reporter gene. A high level of GFP fusion protein was detected predominantly in the nuclei of most, if not all, somatic cells. Shown here is the presence of LIN-40A::GFP in vulval cells, the anchor cell (AC) and many other gonadal cells. (E,F) The expression pattern of a lin-40b::gfp reporter. LIN-40B::GFP was found to be present at a lower level than LIN-40A::GFP in both the cytoplasm and the nucleus. Ventral is downwards and anterior is towards the left. Scale bars: 10 µm.