Developmentally regulated transcription factor which binds and recognizes the enhancer DNA sequence 5'-TGA[CG]TCA-3' (PubMed:23437011). Plays a role the development of the reproductive system, controlling events including anchor cell (AC) fusion and invasion (PubMed:15960981, PubMed:17488621). Regulates downstream transcriptional targets, including zmp-1, cdh-3, him-4 and mig10b, to promote the removal of the gonadal basement membrane during AC invasion (PubMed:15960981, PubMed:24553288). Regulates aff-1 expression to promote AC fusion (PubMed:17488621). With jun-1 regulates egl-1 and lin-12 expression to allow uterine cell specification and development (PubMed:17942488). Required for ovulation (PubMed:19570917). Controls plc-1 expression in the spermatheca to regulate spermathecal valve dilation (PubMed:19570917). Acts with hda-1 as a downstream repressor of the kgb-1 mediated stress response pathway that transcriptionally represses genes involved in the response to heavy metals, such as kreg-1 (PubMed:23437011). Homodimer (PubMed:23437011). Heterodimer; with jun-1 (PubMed:17942488). Interacts with kgb-1 and hda-1 (PubMed:23437011). Additional isoforms seem to exist. Expressed in anchor cells (PubMed:15960981). Isoform a is expressed in somatic gonad cells that neighbor anchor cells (PubMed:15960981, PubMed:19570917). Isoform b is expressed in vulval cells, the uterine cells that neighbor anchor cells and the spermatheca (PubMed:15960981, PubMed:19570917). Detected before the L2 molt stage (PubMed:15960981). Expressed throughout ventral uterine intermediate precursor cells (PubMed:17942488). May be phosphorylated by kgb-1. Phosphorylation at Thr-440 increases sensitivity to heavy metal stress. Phosphorylation inhibits homodimer formation, and promotes association with target promoters. Animals are sterile and display a protruding vulva phenotype (PubMed:17942488). Animals have uterine defects lacking both a uterine lumen and a utse-like process; subsequently fail to develop a differentiated uterus. Furthermore, uterine seam cell genes egl-13 and lin-11 are not expressed during late larval development (PubMed:17942488). At the L3 developmental stage, AC display either failed or delayed invasion leading to the defective removal of the gonadal basement-membrane (PubMed:15960981, PubMed:17488621). AC do not fuse (PubMed:17488621). AC specific expression of lin-3 is increased, but zmp-1, him-4 and aff-1 expression is undetectable and cdh-3 expression is reduced (PubMed:15960981, PubMed:17488621). RNAi-mediated knockdown of both isoforms results in sterility, a protruding vulva and exploded through the vulva phenotypes (PubMed:17942488, PubMed:19570917). Animals have an undifferentiated uterus and lack uterine egl-13 expression (PubMed:17942488). Animals also display an endomitotic oocytes phenotype, which is due to improper distal spermathecal valve dilation and reduced plc-1 expression in the spermatheca (PubMed:19570917). Animals have no mig-10b expression in AC (PubMed:24553288). RNAi-mediated knockdown of isoform b results in an everted/protruded vulval phenotype in adults (PubMed:23437011). Belongs to the bZIP family. Fos subfamily.