Synthetic multivulva (synMuv) class B protein (PubMed:7982579, PubMed:8054684). SynMuv proteins are required to repress the induction of vulval development (PubMed:7982579, PubMed:8054684, PubMed:11463372). Acts redundantly with SynMuv class A protein lin-15A to negatively regulate vulval development (PubMed:8054684). Regulates let-23 basal activity (PubMed:8054684). No obvious vulval development defects (PubMed:8054684, PubMed:11463372). Double knockout with the synthetic multivulva class A protein lin-15A results in a multiple vulva (Muv) phenotype (PubMed:8054684). Double knockout with the programmed cell death regulator mcd-1 results in 100% lethality during the L1 stage of larval development (PubMed:17237514). The proteins lin-15A and lin-15B are produced from a single precursor mRNA with non-overlapping transcripts where lin-15B is the upstream transcript and lin-15A is the downstream one. The precursor mRNA is cleaved at the polyadenylation site and a 22-nucleotide SL2 leader sequence is trans-spliced to the 5'-end of lin-15A to allow its translation.